MAU is the standard measure of reach. Companies define "active" differently: some count any app open, others need a login or a swipe. Always check the definition before comparing apps.
For a dating app, MAU in a given town matters more than the global total. A member only benefits from people they could realistically meet, which is why liquidity is measured locally.
Pricing for many platforms, including per-member fees, is based on monthly active members, so dormant accounts usually cost nothing.