[Rebelgecko]

I think that's an oversimplification of a complicated issue. It's certainly possible that the NASA administrator chose to go with Morton Thiokol to keep congressmen from Utah happy, but as far as I know there's no proof that there was any "deal", and there's plenty of technical reasons to go with a segmented design (although there's tradeoffs).

One of the bidders on the contract actually wanted to make a monolithic SRB, but that brings a new set of problems and limitations, especially at large sizes (you can look up the Aerojet 260" for some more info).

The shuttle SRBs were built in 7 segments, some of which were joined together at the factory. The multisegment design was based on the flight-proven Titan SRBs, which supposedly would help with R&D costs. However manufacturing constraints (if the SRB just used the Titan design and scaled it up, they'd need bigger hunks of metal than anyone was casting at the time) and design tweaks led to changes that degraded O-Ring performance and potentially kept both primary and secondary O-rings from being properly seated. There was really a whole confluence of things that went wrong, and a lot of missed opportunities to fix any one of the issues that led to O-ring failure.

Plenty of people still use segmented SRBs today, especially for their modularity. The (first version) of the SLS boosters are based on the shuttle design, with extra segments stuck added on.