In the case of taxpayer funded deployments (i.e. government acquisitions) it's generally due to being built by the lowest bidder, coupled with an inadequate incentive structure to fix. This may also be the case in some corporate deployments.
It’s also being designed and implemented in a situation where 5 people plan and oversight the work of 1 person-ish. IT is pretty horrible about having lots of know-nothings with shiny job titles telling one or far fewer people who actually do the work and know what is possible that their technical objections or restrictions are false/made up/etc.
