As far as I know, forward has remained the same throughout.
I started riding off road on various bikes, bigger and smaller wheels make as much sense as not to me.
There is a good argument for smaller for certain courses and terrain where larger will limit you, but most seem to ride on prepped trails these days where everything is a little ironed out and the merits of large or small are more to do with other factors.
The weight penalty is of more concern to me than the slacker angles and things I have heard mentioned like gyroscopic effect, blah, blah, blah. Of course your Carbon 29-er is lighter than yer CroMo 26-er as a rule, but on a cost comparison basis 26-ers come in a little less expensive. That remains the deciding factor for a lot of us.
If you look outside the world of MTBs you would find most older bikes having larger wheels.
I think tyre availability was a factor, but one of several.
The doctor diagnosed me with hereditary diarrhoea. I can't understand, I wear a kilt.