why are they desired?

desired , they are hard to get away from,
As all new bikes with very rare exceptions, are indexed,
as you all have the engines of consumerism making them
standard on the bikes in the shops .
they help people who do not want to think about math, of ratios and proportions ,
just an easy to harder 1,2,3.. so increase sales.

I'm a bar end shifter, myself, even the old race style bike has them..
but Yea, OEM builds it is where the component market went..

Touring bike builders often fit the index bar end, non index front ,left,
lets you run either road or mountain cranksets, and FD.
and trim the cage after rear shifts, so it won't drag against the chain...

I did not have to follow.. my last bike purchase didn't even use derailleurs.