Why are thumb shifters so prized in the retrobike community?

[greencat]

Can you explain this please?

I was thinking that the only benefit I can think of with trigger ones is being able to maintain your grip and thought that trigger shifting doesn't necessarily have to be indexed so wondered if there are indeed friction trigger shifters which give the benefits of the maintained grip with all the usual benefits of friction shifting.

They looked a bit like this (but black all over IIRC)

Yes, trigger shifting does indeed help maintain grip/avoid having to shift it. I am going to say that indexed gears with trigger shifters is a solved problem now - and mostly very easy to use and set up. I resisted for many years, but frankly they just work. Hardly surprising after 30 years of R&D. I've got a deore 10 spd trigger system on my Whyte, and it still runs perfectly after 18 months - no adjustments whatsoever.