You're also talking about fundamentally different kinds of rocket boosters. The Space Shuttle used solid fuel boosters, which are basically nothing except a tube packed full of energetically burning material, an igniter to light said material, and a nozzle for the generated gases to come out. They couldn't throttle, couldn't gimbal, couldn't shut off or restart, didn't use cryogenic fuel so didn't need insulation, didn't rely on pressurized fuel so they didn't need turbopumps... In fact, as far as I know they basically didn't have any moving parts at all!
You ever flown a model rocket, like an Estes? That little tube of solid grey gritty stuff that you use to launch the rocket is basically a miniature version of the solid fuel boosters on the Space Shuttle. The shuttle boosters were obviously bigger, and were a lot tougher (which made them unacceptably heavy for something like the Falcon 9's first stage) so they could survive the water landing, but fundamentally they were basically just cylindrical metal tubes with a nozzle at the bottom.
Despite that, reconditioning them for re-use was still so expensive that it's unclear if the cost was worth it. Now, of course, they cost a lot less to build than a Falcon 9 first stage, but every one of the Falcon 9 first stage's nine Merlin 1D engines is many times as complicated as the entire solid booster used on the Space Shuttle. Even the first stage tank is much more complicated, since it needs to take cryogenic fuels and massive internal pressurization.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
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