This is not technically true (but often true).

Water vapor is a gas and is much smaller than the "leaks" of particles. A perfectly sealed filter (like an elastomeric mask with high fit factor) will still release a ton of H20.

EVIDENCE: The exhaust from PAPRS and viralhelmets.com has a ton of moisture.

That is only a concern for medical grade masks. Most masks that people wear are to slow down the air, not filter the air.