CPAs are probably more talented than I am, which is where the root of my comments (quoted above) lay.
I'm personally able, more or less, to keep up with the annual federal changes and my state's changes, especially as they apply to my family and my clients as a Tax Aide volunteer preparer. As not-a-CPA, that's all I need to do. Even doing that requires me to read up on stuff throughout the year, and attend several weeks of training every January.
Keeping up with multiple states' changes as some real CPAs do would seem extremely challenging. It would seem even more challenging to be good enough to remember all the quirks of all the states (especially the new ones from time to time) to ask all of the clients all the right questions to elucidate whether or not those quirks apply to them and collect the right data and prepare the return well.
I'm fairly certain that CPAs have continuing education requirements, and I'm betting that is the reason why. I'm sure they also have colleagues who have varying degrees of knowledge and specialization about various states and various tax topics (that's the way it is in Tax Aide anyway - person X knows about education credits, person Y about disability pensions, etc.) I think that's all well and good.
And I'm also pretty sure that a CPA could adequately and correctly prepare an out of state return, especially if they live in a nearby state (like WA) or if my state were an important one tax wise (ID, it isn't really).
But with all that said, I'd prefer an Idaho firm over say, a Tennessee firm because I think they'd be better equipped to remember, for example, that Idaho taxpayers for 2021 are supposed to add their $300/$600 non-itemizing charitable cash deductions to their standard deduction on line 16 - an errata published on the state tax commission's website but not in the Idaho state instructions (which I doubt they will revise). If the Tennessee firm missed something like that, the tax return would still likely be accepted and no penalties would be applied, but the individual would still pay a bit more tax.
I also - again, this is just my personal opinion - would point out the second sentence of the quoted portion above. I personally want to go in person, at a table, with paper and pencil/pen, to go over any topics that are complex. You can do that over Zoom and so forth with a Tennessee firm, but it's not my preference.
And of course, to be clear, I like Tennessee as a state and Tennessee residents in general of the ones I've met.