My opinion is that one can do whatever they want with their stake: if you earned it, it's yours, and that's ok.
However, Hive right now is in a position where it needs people working to make it thrives. Selling everything, not building your HP, shows everyone that (probably) you don't care about Hive, and that, at the very least, is bad because people reading your articles, or following you, or looking at your nice earnings, might think that that's how Hive works.
Maybe one day we will be able to have huge influencers selling all (or almost all) their stakes and that will be a drop in the ocean none will care about... who knows.
But that's not the case, yet.
People coming here have to understand that if you want to be a (good) part of Hive, you can't only think about extracting as much value as you can.
Instead, you have to give something back. Building your HP, showing that you care about Hive and what you earned here, is a good first step in the right direction.
It can't be the only criteria to support someone, but I'm happy to see that, lately, a lot more people are starting to consider it as one of the criteria to consider.
To get something you should give back something.
If you are not bringing new users, or building awesome dApps, or engaging (in a meaningful way) with others, well, you should at the very least build your HP to support others, otherwise I can't see why you should get my upvote.
People want to earn, but they don't want to take responsibility. They want value attention, but don't want to be scrutinized.
If people could, they would try to get everything without giving anything. Not sure if they don't understand that this can't work long-term... or if they don't care.