Why is this happening? The root cause can be traced to two key factors.
1) Business team gets asked what they want (and don't know)
The business team doesn’t know what they want because they don’t know what is possible. They fall back to what they do know, the current experience, and spend most of the time making certain they don’t lose any “functionality”. This results in the requirements being pretty much what the business has today, with a couple of small enhancements.
2) Technology team implements parts of the ask (because it is all that is needed)
When the technology team gets the requirements, they begin to wonder why all this money was spent to replatform what they have today. Then timelines get squeezed, budgets get cut and the technology team falls back on what they know – their internal systems. Rather than setup the new platform to bring capabilities that the business didn’t ask for (but should have), they deliver on the requirements in a piece-meal way that allows the project to go live but limits the potential of the solution.