Long time ago i worked on WiMAX devices which was a competing standard for the term “4g” from ieee and while it was simpler it wasn’t a whole lot simpler and performance sucked, so there’s that

When GSM was created by the European telcos (at the time they were still monopolies) a lot of care went into making the different parts decoupled with defined standards between the different parts, so that they could pit vendors against each other to avoid getting locked into vendor silos. This contributes a lot to the standards bloat since every interface needs to be defined.

In contrast there were the Qualcomm CMDA standards which were all proprietary and in-house, which had some upsides, but in the end carriers preferred the open standard with vendor competition.

There's a book called "GSM and UMTS: The Creation of Global Mobile Communication" about the history which is really interesting.