Because Everest is on the tick list that non-climbers recognize and because a lot of the lower mountains are much, much harder and nobody will guide them. There is a reason Gasherbrum IV has only been climbed four times (five if you count the 1985 Kurtyka-Schauer route, which is still regarded as one of the most impressive alpine climbs ever), Gasherbrum III has been climbed twice, Khunyang Chhish twice, Bainthha Brakk twice, Latok I. There are lots of other "obscure" remote peaks with one or zero ascents that are way harder, more adventurous, and serious than Everest. Climbing Everest solo post-monsoon by a new route in 1980, or from the north as a party of two without carrying ropes or sleeping gear in 1986 is absolutely impressive. Trudging up the normal route with support does not count as climbing to anyone who climbs.

Messner's solo ascent is generally considered to be the last time a climber was truly alone on the mountain.