Why they can't provide better solution and solve the problem with speed of transactions and scalability?
Bitcoin added SegWit last year. Now Lightning Network is under development. All of them are additions that help solving these problems.
These problems are not easy to solve and everything needs time to be developed and tested.
You need patience, you need to read more and you need to understand that cryptocurrencies are still young and under development. At least for Bitcoin we seem to be on the right track.