Well TBF, ATLUS tends to use PCB Productions (they've used others mind you, but this one pops up the most frequently in the game credits of ATLUS games), for voice acting in a lot of their localizations. So it's inevitable that you'll have a lot of casting overlap between games.
EDIT: I just looked at production credit list that PCB Productions has for VA production involved with games. And yeah most ATLUS games, even if they're uncredited. Has been done with PCB, all the way back to the PS1 days.
Here's a list of their credits from their website, if your curious.
I'm well-aware of PCB, but they have nothing to do with the actual casting. Atlus isn't like Funimation in the sense that they do all their production in-house, mostly using their own stable of actors; they really have no real reason to stick to some pre-defined list, particularly when it's not like PCB would mandate one.
Since Atlus joints are technically classified as non-union, despite them still allowing some union folks in, a good amount of the castings are going to be booked via the talents' agents sending out demo reels; in some cases, there might not even be an audition period. The others are done when actors are recommended by other talents already booked, such as when Sam Riegel recommended his sister for Marie. In these cases, it can be hard for the people who are in charge of deciding what voices go with which characters, particularly when they usually neither have the time nor the budget to extend that period out.
To give you an idea, the recommended length of a voice demo is a minute; most people don't listen for even ten secondsbefore making a judgment. The reason being, most projects can't afford to laze about. VO can be a mess, but it still strikes me as odd that they wouldn't try to differentiate their characters more. They're clearly not against the idea of bringing in new blood, such as when they got Michelle Ann Dunphy, who got her start in amateur voice acting communities, for Margaret. So it just strikes me as odd that they're constraining themselves like this, when there's actually a pretty wide pool they can choose from, even if not all of them have a ton of credits to their name.
Some things are unavoidable, especially when decisions need to be made without knowing what the other side of Atlus will do years down the line, but some of their decisions just seem funny to me, especially when some seemed to have obvious and, (in my opinion), better fixes.
I just hope the major characters for 5 don't have any returning talents, unless they can really Maj their voices well.