Depends on where you are. Underdark Drow city of Menzoberranzan, probably quite common for more prominent houses, but still not as common as in BG3. Host Tower in Luskan - VERY common. Some defunct ruin of an ancient elven city. Might be common there too.
So it depends, honestly. If they had a decent explanation for it, I don't think it would be as big an issue, AND if they didn't allow you to use them from anywhere without cost or potentially running into dangers.
Example: Champions of Norrath 2. Portals everywhere. You were bouncing from plane to plane. BUT, they were level markers. You had to physically walk to each and every portal and you pretty much used one only when you had cleared the level.
The problem with BG3 is that you can just willy nilly use them. There's no limit or nothing. Now, if they did something like, "You must find special crystals that activate them. You spend one crystal per use.". That would make more sense.
See, in FR, portals are powerful magic. There is usually something required to use them. You don't just see one and go, "Hey. I can teleport now to anywhere.". You need to actually be able to use magic read it, understand it, or have some magic items to activate them.
