The real reason is that different businesses have different needs. No one company knows all these needs in the beginning, so they build and keep tacking on to their existing solution. They can't easily refactor and break UI changes for their existing clients, so it's end up a big ol mess of everything.
Given everything most enterprise companies know, they can design cleaner simpler software, but the reality is there's no time to stop when you have a business to run for the big ol design. When that is done most of their customers are pretty unhappy, something as simple as changing UI change can be very expensive for your clients, they might have to retrain thousands or tens of thousands of their users. Something as simple as an upgrade, if not a zero time upgrade can affect tens of thousands of users. Enterprise is not as stupid as folks make it out to be. There's a reason they got to being enterprise and make a lot of money, they are a different kind of smart.
Given everything most enterprise companies know, they can design cleaner simpler software, but the reality is there's no time to stop when you have a business to run for the big ol design. When that is done most of their customers are pretty unhappy, something as simple as changing UI change can be very expensive for your clients, they might have to retrain thousands or tens of thousands of their users. Something as simple as an upgrade, if not a zero time upgrade can affect tens of thousands of users. Enterprise is not as stupid as folks make it out to be. There's a reason they got to being enterprise and make a lot of money, they are a different kind of smart.