Agreeing with everyone (especially Forget... when it comes to "suitish or notrumpish"? But a reminder that while 1D-3D frequently gets passed, 1D-2D frequently ends up in 3NT anyway) when RHO passes. These days, RHO often doesn't pass.
When RHO comes in, I am much more likely to raise on 4 than bid NT. I could have no stopper in RHO's suit. I could "see" the cross-ruff with a singleton in RHO's suit (or with 4!). I could just want NT, if played, to be played by partner, so the stronger hand is concealed and RHO-who-doubled has to make the opening lead (LHO will know which suit to lead, RHO has more of a guess!).
But the big reason that will get me to raise-on-4 is that I see the auction getting competitive, and my meta-agreement #1 (or very close to #1) is "in a competitive auction, support with support." If I have a one-bid hand, it's frequently more important to tell partner "we have a fit" than "I have a stopper". If I have a two-bid hand, I have tools (cuebid raise/overcall, 2NT/double) to show a strong raise, which I can make and then make a reasonable second call hearing partner.
Note that if you are playing matchpoints, the "race to 1NT" is definitely a thing: 1NT making 1 is the same as 2D making 2, and 1NT making 2 beats 2D making 3. So that is an argument against a non-obvious raise.
Of course, like everything in bridge bidding, it is more important to be on the same page as partner than it is to confuse, but be technically correct. It might be right to raise to 3 on 4 cards, a stiff, and a 7-count; but when partner's 18 bids 3NT counting on the diamond tricks and only takes 8, "right" is cold consolation.