Why would researchers think that the Delta Variant is the last wave of Covid?

 The main reason is likely the Spanish Flu of 1918 to 1920. Since that virus killed 50 million people on earth from Spring of 1918 until the end of 1920 they might believe this virus is similar and will create enough herd immunity by 2022 to start ending.

The problem with this thinking is this Covid through it's variants isn't acting like the Spanish Flu at all and hasn't all along in that it has kept creating new variants over and over again around the world. Even now we have the MU Variant from Columbia showing up which is also very infectious like the Delta Variant too.

So, from my point of view thinking that the Delta is the last Variant is ONLY wishful thinking to keep people around the world from committing suicide rather than deal with any more of this.

I think instead it would be more useful to start preparing for this to be endemic to the world like we did with AIDS. By preparing for the likely inevitable we gird ourselves for a more difficult future but in the end this realism might save millions of lives ongoing.

If people believe this is never going to end and that a vaccine is the ONLY way to stay alive through Variant after Variant then this in itself will save millions and billions of lives.

By the way I presently believe more than 50 million people have already died of this on earth and the number might be as high as 100 million people actually so far. However, I don't expect to read that anywhere much simply because just this news might kill a lot of people through suicide if they cannot handle it.

I try to give people the truth here so that they have enough truth to make good decisions in order to find ways to stay alive through all of this. 

If you don't have the full truth you cannot make good decisions in the first place in trying to stay alive.