Before covid the orderbook was mostly 100-400 contracts for every tick on the ES. Now it's often 10-40 and on my tick charts I frequently see 1 tick gaps before they backfill which rarely ever happened before March.

Is this solely because of the volatility which came with covid and also now the upcoming election? Or is it also because HFT changes the ES more and more? So will the orderbook get thicker again after covid and election is behind us or will it become thinner and thinner over the next months and years?

Fewer human traders - fewer resting orders.

This covid market sent into retirement a lot of old school traders with decent sized accounts but prone to martingaling.