The answer to why is almost always because that is the limit of talent available to the organization at the time with the given technology options available. Its really that simple.

In some cases there are many options and great talent is readily working on the problem for the given organization. Its nice to have options, but this is an exceedingly rare scenario. For example there are tons of options available today, but from reading HN job posts it looks like the answer is still a CRUD app that does some SAAS solution with React, AI, and Python. I could guess that and be right more than 60% of the time, which is extraordinary considering these businesses have thousands of technology combinations and unlimited ideas to pick from. Its all about the talent available, but when I say talent I just mean people because when you are that restricted it isn't very talented.