Well first off, i think there is an argument that creating & simulating algorithms is CS stuff anyways.
Second its often (not always) a lot more work to test scalability with benchmarks than it is to theoretically analyze.
Especially because people are often worried about both average case and worst case. The input that takes down your site is not the one you expect, and simulating realistic load is difficult.
It can also be pretty hard to compare benchmarks. You probably dont want to test every algorithm known to man yourself, but two separate benchmarks on diff hardware and diff conditions cannot be reasonably compared. More abstract analysis can (to an extent anyways)
Second its often (not always) a lot more work to test scalability with benchmarks than it is to theoretically analyze.
Especially because people are often worried about both average case and worst case. The input that takes down your site is not the one you expect, and simulating realistic load is difficult.
It can also be pretty hard to compare benchmarks. You probably dont want to test every algorithm known to man yourself, but two separate benchmarks on diff hardware and diff conditions cannot be reasonably compared. More abstract analysis can (to an extent anyways)