When I learned how to drive, manual transmissions were higher performance and better fuel efficiency: side by side comparisons of the exact same model of car would show better 0-60 and quarter mile times, while having slightly better EPA fuel efficiency ratings, for the manual transmission.

At some point, though, the sheer number of gears in an automatic transmission surpassed those in the typical manual gearbox, and the average automatic today has 6 gears, up to 9 in some Mercedes and 10 in certain Ford and GM models. So they could start selecting gear ratios for better fuel efficiency, without "wasting" a valuable gear slot. There was a generation of Corvettes that was notorious for having a 6th gear that was worthless for actual performance but helped the car sneak by with a better highway fuel mileage rating.

And the automatics became much faster at shifting gears, with even the ultra high performance supercars shifting to paddle shifters where the driver could still control the gear, but with the shifting mechanism automated. Ferrari's paddle shifter models started outperforming the traditional stick shift models in the early 2000's, if I remember correctly. As those gear shifting technologies migrated over to regular automatics, the performance gap shrunk and then ended up going the other way.

At this point there's not enough reason for a true manual stickshift transmission. It's no longer faster or more economic, so it's just a pure fun. Which is fine, but does make it hard to actually design one for any given model of car.