The shuttle’s solid rocket boosters splashed down in the ocean via parachute, and were recovered and reused. The main engines and thrusters/rcs were also reused. Only the external tank was disposed. The issue with the shuttle (among many) was that the reuse was not actually economical due to the maintenance required between each launch.

> the reuse was not actually economical

Well - yes :) That is what reusable actually means. Anything's "reusable" if you spend enough money. The idea is it's worth doing.