That's exactly what gatekeeper means: entities that control access to something (in this case financial capital on terms suitable to buy property, but equally it can be social capital to access in-group acceptance, etc).

This control of access to resources is where the name comes from, and its broader use (rather than the highly specific social use we see online) is recently exemplified in the EUs Digital Markets Bill describing large search providers (like google) and social media (facebook) as gatekeepers.

Makes sense to me. Is a mortgage officer not a gatekeeper of the bank's capital?