why is pants always rebuilding the requirements.pex files, even if I just run the test 2 sec before?

21:19:42.99 [INFO] Canceled: Building pytest.pex from <resource://pants.backend.python.subsystems/pytest.lock>
21:19:44.10 [INFO] Completed: Building pytest.pex from <resource://pants.backend.python.subsystems/pytest.lock>
⠐ 25.58s Building requirements.pex with 6 requirements: diffusers>=0.33.1, etils[epath], jaxtyping, pydan

this is the output of running

pants test projects/xxxx/tests/xxxx/utils/test_torch.py