It does a lot of module imports. Most of those probe the filesystem.

Try "python -vv -c 'pass'" - I'm only showing the first few dozen lines, and I've trimmed some of the paths for conciseness:

% python -vv -c 'pass'
import _frozen_importlib # frozen
import _imp # builtin
import '_thread' # <class '_frozen_importlib.BuiltinImporter'>
import '_warnings' # <class '_frozen_importlib.BuiltinImporter'>
import '_weakref' # <class '_frozen_importlib.BuiltinImporter'>
# installing zipimport hook
import 'zipimport' # <class '_frozen_importlib.BuiltinImporter'>
# installed zipimport hook
import '_frozen_importlib_external' # <class '_frozen_importlib.FrozenImporter'>
import '_io' # <class '_frozen_importlib.BuiltinImporter'>
import 'marshal' # <class '_frozen_importlib.BuiltinImporter'>
import 'posix' # <class '_frozen_importlib.BuiltinImporter'>
import _thread # previously loaded ('_thread')
import '_thread' # <class '_frozen_importlib.BuiltinImporter'>
import _weakref # previously loaded ('_weakref')
import '_weakref' # <class '_frozen_importlib.BuiltinImporter'>
# miniconda3/lib/python3.7/encodings/__pycache__/__init__.cpython-37.pyc matches miniconda3/lib/python3.7/encodings/__init__.py
# code object from 'miniconda3/lib/python3.7/encodings/__pycache__/__init__.cpython-37.pyc'
# trying miniconda3/lib/python3.7/codecs.cpython-37m-darwin.so
# trying miniconda3/lib/python3.7/codecs.abi3.so
# trying miniconda3/lib/python3.7/codecs.so
# trying miniconda3/lib/python3.7/codecs.py
# miniconda3/lib/python3.7/__pycache__/codecs.cpython-37.pyc matches miniconda3/lib/python3.7/codecs.py
# code object from 'miniconda3/lib/python3.7/__pycache__/codecs.cpython-37.pyc'
import '_codecs' # <class '_frozen_importlib.BuiltinImporter'>
import 'codecs' # <_frozen_importlib_external.SourceFileLoader object at 0x10dd44c90>
# trying miniconda3/lib/python3.7/encodings/aliases.cpython-37m-darwin.so
# trying miniconda3/lib/python3.7/encodings/aliases.abi3.so
# trying miniconda3/lib/python3.7/encodings/aliases.so
# trying miniconda3/lib/python3.7/encodings/aliases.py
# miniconda3/lib/python3.7/encodings/__pycache__/aliases.cpython-37.pyc matches miniconda3/lib/python3.7/encodings/aliases.py
# code object from 'miniconda3/lib/python3.7/encodings/__pycache__/aliases.cpython-37.pyc'
import 'encodings.aliases' # <_frozen_importlib_external.SourceFileLoader object at 0x10dd67d10>
import 'encodings' # <_frozen_importlib_external.SourceFileLoader object at 0x10dd440d0>
# trying miniconda3/lib/python3.7/encodings/utf_8.cpython-37m-darwin.so
# trying miniconda3/lib/python3.7/encodings/utf_8.abi3.so
# trying miniconda3/lib/python3.7/encodings/utf_8.so
# trying miniconda3/lib/python3.7/encodings/utf_8.py
# miniconda3/lib/python3.7/encodings/__pycache__/utf_8.cpython-37.pyc matches miniconda3/lib/python3.7/encodings/utf_8.py
# code object from 'miniconda3/lib/python3.7/encodings/__pycache__/utf_8.cpython-37.pyc'
import 'encodings.utf_8' # <_frozen_importlib_external.SourceFileLoader object at 0x10dd44bd0>
import '_signal' # <class '_frozen_importlib.BuiltinImporter'>
# trying miniconda3/lib/python3.7/encodings/latin_1.cpython-37m-darwin.so
# trying miniconda3/lib/python3.7/encodings/latin_1.abi3.so
# trying miniconda3/lib/python3.7/encodings/latin_1.so
# trying miniconda3/lib/python3.7/encodings/latin_1.py
# miniconda3/lib/python3.7/encodings/__pycache__/latin_1.cpython-37.pyc
matches miniconda3/lib/python3.7/encodings/latin_1
... many, many more lines omitted ...

This can be sped up a lot using a zipimport of the Python standard library, https://docs.python.org/3/library/zipimport.html?highlight=z... , where all of the standard library is put in a zipfile. Then there's a file access to get the zip metadata.

One of the things that bugged me in Python2 was that every startup imported UserDict:

# trying python2.7/UserDict.so
# trying python2.7/UserDictmodule.so
# trying python2.7/UserDict.py
# python2.7/UserDict.pyc matches python2.7/UserDict.py
import UserDict # precompiled from python2.7/UserDict.pyc

This is because os.environ was an instance of UserDict:

% python2.7 -c 'import os; print(os.environ.__class__.__bases__)'
(<class UserDict.IterableUserDict at 0x1029b14c8>,)

Under Python3 this is spelled collections.abc.MutableMapping:

% python3 -c 'import os; print(os.environ.__class__.__bases__)'
(<class 'collections.abc.MutableMapping'>,)

which triggers its own set of imports:

# trying python3.6/collections/abc.cpython-36m-darwin.so
# trying python3.6/collections/abc.abi3.so
# trying python3.6/collections/abc.so
# trying python3.6/collections/abc.py
# python3.6/collections/__pycache__/abc.cpython-36.pyc matches python3.6/collections/abc.py
# code object from 'python3.6/collections/__pycache__/abc.cpython-36.pyc'
import 'collections.abc' # <_frozen_importlib_external.SourceFileLoader object at 0x103c2ecf8>

There's better performance using SDD than a HDD, which is in turn better than using a networked filesystem.