Thanks for being patient and hanging in there with me.
My long-term players can back me up on this: There's been a trend in my DM style, through the years. I've become a more focused and disciplined DM, not so much flying by the seat of my pants. But it's a constant, never-ending struggle. I'm constantly fighting my natural 'everything but the kitchen sink' tendency. Right now, in this moment, it sounds really fun to me: "A wizard casts a spell and everyone wakes up as a bullywug! Welcome to Bullywug Heroes of Hornpipe, my froggy friends!" But then the little voice tells me, stop, don't do that. Stay focused. Stick to the plan.
Like right now, for example: I tried to write the two most boring NPCs ever. Darby's favorite color is beige and his favorite food is oatmeal. Mike only says one word. And yet, right now in the moment, my natural DM tendency, that I'm constantly fighting to reign in: Maybe Mike and Darby are secret lycanthropes, plotting to overthrow the government. Maybe there's a secret door in the cellar, that leads to an ancient tomb. And in the tomb is a teleporter that goes to the Moon, which is ruled by talking cats, and the cats ride around on dinosaurs, and the dinosaurs have laser beams...
Which is a long winded way of saying, when I say "no" to something like bullywugs, it's not just the bullywugs... it's the avalanche of other ideas that will come pouring out, if I go off script and lose my focus. It's good for my real-world mental health, for things to be orderly in my fantasy world.
These days, it's more my DM'ing style, that instead of introducing all the bullywugs as a playable race, maybe the party encounters a unique creature, The Bullywug, who becomes an important and memorable NPC in the campaign (like Puddleglum in the Narnia books).
If I made one mistake in retrospect: I intentionally didn't stock any NPCs or sentient species on the 1st dungeon level, maybe I shouldn't have done that. Role-playing conversations with NPCs is an important part of your enjoyment of the game, and I see now, it would have been fun to give you players someone (or something) to talk to on the 1st dungeon level. Don't worry though: There are lots of interesting role-playing encounters on the deeper dungeon levels! You either need to get across the water on dungeon level 2, or down to levels 3 (and beyond).