There are many species of stink bug in Maryland, but the invasive Brown Marmorated Stink Bug has had lower populations in recent years (at least anecdotally, as no one is doing surveys as far as we know). Population declines like this can be due to many factors, including predation and weather impacts. As a non-native species, it's probably just being absorbed into the ecosystem in terms of other organisms learning to eat them and parasitoids (like tiny wasps that kill them) also increasing in number.

Miri