Inevitable? No. A process repeated over and over again? Yes.

The top down approach isn't organic, but it's a process that develops from the online group dynamics. It's not a right wing or left wing issue so much, as it's an issue with authoritarians. In any group that leans particularly in a certain direction, as reddit certainly did lean towards the left heavily. The number of extreme voices will echo heavily towards one side, react against the extreme voices on the other side, and slowly push the dynamic towards more censorship, more extreme positions, and more authoritarian approaches.

Extremists by necessity must adopt authoritarian approaches to enforcement because by nature of being extremist, they're agendas do not line up with the majority of people, even on their side of the fence. Eventually the extremist side that has the largest support base will be able to seize power, ostensibly against some threat or crisis, as you saw happen swiftly on reddit with the Trump election result reaction and the COVID discussion, which is used as an excuse to purge all dissent.

Such policies are not particularly effective in the long run, as extremism must always have a crisis to justify authoritarianism to the larger society, and once the crisis is abated, they will lose their authority base, but the extremist will not abandon their authoritarian approaches as that represents compromise, which is not something an extremist is willing to do. So they will hold power with an iron fist becoming increasingly more and more cruel in their wielding of power until such a time as something gives and they are removed.

In context of Reddit. It is at the end of the day. Not very important. And the power of a moderator doesn't extend far beyond their own website, so people will simply take the path of least resistance and leave, giving the moderator power over what is essentially an empty website. Much like how if a teetotaler is in charge of planning the Christmas party, some other person will just start their own party with beer.