BUG: Transpose changes dtype from object to timedelta/datetime

[phofl]

Pandas version checks

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Reproducible Example

df = DataFrame({"a": [pd.Timedelta("1 days"), pd.NaT, pd.Timedelta("2 days")]}, dtype=object)
df.T.dtypes


0    timedelta64[ns]
1     datetime64[ns]
2    timedelta64[ns]
dtype: object

Issue Description

I'd expected this to return object, but this was changed in #26285

Expected Behavior

The whatsnew looks like the fix was tailored to avoid raising an error, any other motivations?

Installed Versions

Replace this line with the output of pd.show_versions()

[jbrockmendel]

I'd expect object too