Pandas BUG: DataFrame.mean(axis=1) fails but Series.mean works incase of pandas Nullable integer dtype

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[x] I have confirmed this bug exists on the latest version of pandas.
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Note: Please read this guide detailing how to provide the necessary information for us to reproduce your bug.

Code Sample, a copy-pastable example

>>> import pandas as pd
>>> df = pd.DataFrame({"a":[1,2,3, 4], "b":pd.Series([1, 2, 4, None], dtype=pd.Int64Dtype())})
>>> df
   a     b
0  1     1
1  2     2
2  3     4
3  4  <NA>
>>> df.mean()
a    2.500000
b    2.333333
dtype: float64
>>> df.mean(skipna=False)
a     2.5
b    <NA>
dtype: object
>>> df.iloc[3]
a       4
b    <NA>
Name: 3, dtype: Int64
>>> df.iloc[3].mean(skipna=True)
4.0
>>> df.iloc[3].mean(skipna=False)
<NA>
>>> df.mean(axis=1, skipna=False)
Traceback (most recent call last):
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/nanops.py", line 1415, in _ensure_numeric
    x = x.astype(np.complex128)
TypeError: must be real number, not NAType

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/frame.py", line 8649, in _reduce
    result = func(values)
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/frame.py", line 8570, in func
    return op(values, axis=axis, skipna=skipna, **kwds)
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/nanops.py", line 71, in _f
    return f(*args, **kwargs)
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/nanops.py", line 129, in f
    result = alt(values, axis=axis, skipna=skipna, **kwds)
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/nanops.py", line 563, in nanmean
    the_sum = _ensure_numeric(values.sum(axis, dtype=dtype_sum))
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/nanops.py", line 1418, in _ensure_numeric
    x = x.astype(np.float64)
TypeError: float() argument must be a string or a number, not 'NAType'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/nanops.py", line 1415, in _ensure_numeric
    x = x.astype(np.complex128)
TypeError: must be real number, not NAType

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/generic.py", line 11466, in stat_func
    func, name=name, axis=axis, skipna=skipna, numeric_only=numeric_only
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/frame.py", line 8660, in _reduce
    result = func(values)
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/frame.py", line 8570, in func
    return op(values, axis=axis, skipna=skipna, **kwds)
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/nanops.py", line 71, in _f
    return f(*args, **kwargs)
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/nanops.py", line 129, in f
    result = alt(values, axis=axis, skipna=skipna, **kwds)
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/nanops.py", line 563, in nanmean
    the_sum = _ensure_numeric(values.sum(axis, dtype=dtype_sum))
  File "/Users/pgali/PycharmProjects/del/venv1/lib/python3.7/site-packages/pandas/core/nanops.py", line 1418, in _ensure_numeric
    x = x.astype(np.float64)
TypeError: float() argument must be a string or a number, not 'NAType'

Problem description

When there is a row-wise mean calculation of a nullable interger dtype the operation fails. But the same operation works correctly on a series by doing an iloc on the row.

Expected Output

Output of `pd.show_versions()`

INSTALLED VERSIONS ------------------ commit : 2a7d3326dee660824a8433ffd01065f8ac37f7d6 python : 3.7.3.final.0 python-bits : 64 OS : Darwin OS-release : 19.6.0 Version : Darwin Kernel Version 19.6.0: Thu Jun 18 20:49:00 PDT 2020; root:xnu-6153.141.1~1/RELEASE_X86_64 machine : x86_64 processor : i386 byteorder : little LC_ALL : None LANG : None LOCALE : en_US.UTF-8 pandas : 1.1.2 numpy : 1.17.3 pytz : 2020.1 dateutil : 2.8.1 pip : 20.2.3 setuptools : 50.3.0 Cython : None pytest : None hypothesis : 5.29.0 sphinx : None blosc : None feather : None xlsxwriter : None lxml.etree : None html5lib : None pymysql : None psycopg2 : None jinja2 : 2.11.2 IPython : None pandas_datareader: None bs4 : None bottleneck : None fsspec : None fastparquet : None gcsfs : None matplotlib : None numexpr : None odfpy : None openpyxl : None pandas_gbq : None pyarrow : 1.0.1 pytables : None pyxlsb : None s3fs : None scipy : None sqlalchemy : None tables : None tabulate : None xarray : None xlrd : None xlwt : None numba : None

Comment From: dsaxton

The mean method hasn't been properly implemented yet for nullable ints, but there is this issue https://github.com/pandas-dev/pandas/issues/34754 and this PR https://github.com/pandas-dev/pandas/pull/34814 open addressing that.

cc @jorisvandenbossche

Comment From: jbrockmendel

The problem isn't with IntegerArray.mean, its with df.T being all-object dtype.