In the trem/verb case I think it’s because they used to come together with amps in the past, so there’s several units like that.
Strymon has other units that are the same size and price but only have one effect. The other button is used for tap or favorite. Given that I would argue that in the Flint case you get an effect for free these things are just very expensive.
And don't get me wrong - the Flint is a really solid pedal. Hard to criticize it. If you are a Tremolo nut or Verb Nerd....yeah, it isn't going to do it for you.
But it has a nice usable range of Reverbs, and all the tremolo and more than most would ever need. Still, I never can hear the $300 for it.