Reusing a Shuttle/ SLS SRB by making a parachuted landing on land.

[Nibb31]

Would landing on land (or a landing boat) make the entire SRB reusable, rather than just the steel casing, like it was like when landed on water?

No. A solid surface would make an even harder landing, with increased risk of buckling the steel casings. It would require even larger parachutes, which would be impractical, and the landing would still be violent. Not to mention that the slower you come down, the harder it is to aim for a small area.

And as said previously, there is no land to land on. Orbital launches are deliberately towards the east (because you get a small boost in dV due to the Earth's rotation) and over the ocean (so that a mishap doesn't rain fiery bits on populated areas), which is why Cape Canaveral was chosen as America's main launch site. The risk of launching SRBs over land is too big, they have to launch over the ocean.

And the biggest cost of an SRB is the casting of solid fuel, which is no longer there when its burnt out. It's not like a liquid booster, where the most expensive part is the engine.

[Capt. Hunt]

Yeah, I've seen a deactivated Titan IV booster, basically it's just a bunch of big hollow steel tubes stuck together with O-rings, the shuttle boosters were built basically the same way.

A bit off topic but, I read some place once that the shuttle used solid rockets engines only because it had an already set infrastructure for manufacturing the same thing for ICBMs, and that it was some senator's gimmick to keep his people working or something like that.

You're close, solids were chosen over liquid boosters because of cost, but the "senator's gimmick" you mentioned is what lead to them using the segmented Thiokol boosters rather then a monolithic design from another company (which I can't remember the name of off the top of my head).