I've played through HotDQ, PotA, and the expedition adventures that go along with them and I have always had amazing opportunities to make use of Hold Person.
Then you also know that there are a lot of humanoid foes in those modules at low levels that one would not waste a 2nd level spell slot on. Most are cultist flunkies, kobolds, etc. Only leaders and BBEGs require a Hold Person at low levels. At higher levels, sure. I've already admitted that in a higher level slot, Hold Person starts gaining a lot more traction.
Burning Hands in a second level slot works better than Hold Person against most humanoids in those modules since most humanoids are mooks. So does Thunderous Wave. So does a lot of other area effect spells. Even in your Bugbear example, the most likely result of a second level Burning Hands on two Bugbears tends to result in one Bugbear being half damaged and the other one being quarter damaged. That's 20 points of damage that Hold Person probably will not catch up to for two allied PCs (since they had a chance to hit anyway, Hold Person merely buffs their damage and to hit). If the other two PCs hit the half damaged one, the party is still down one bugbear in a single round and another Bugbear is quarter damaged. If the caster can catch 3 Bugbears, it's even more gravy.
Note: Even Sleep in a second level spell slot will often do better than Hold Person against three Bugbears since there is no save. On average, Sleep will take out a Bugbear and the two other PCs can attack the other Bugbears.
At low level, there are many spells that have a lot more targets that they can affect which can work against humanoids better than Hold Person.
There are always exceptions, but holding onto a prepped spell for those exceptions to come up is a resource expense, one that may or may not pay off most adventuring days.
Just because you had a few good results with Hold Person at low level does not make it a good low level spell. Our party is level 6 and half of them have access to Hold Person and none of them have ever cast it. Possibly that's because we do not have a lot of town adventures in my game, but mostly I think it's because there are often better options at low level.
Nope. Because they wouldn't have auto-critted on the target of Tasha's and the target would get a save after every hit.
While this is true, the foe would still be prone until its turn which means that at least one PC gets advantaged attacks and possibly two. A slight drop in DPR in return for a spell that affects (and the player actually wants to cast on) a lot more potential creatures. Pros and Cons.