There are really many many different types of trades and companies in the market and for different trades, requirements tend to differ. There are just too many trades to even name and even if we are talking about the same trade, different companies tend to operate differently, have different directions or different preferences somehow.
Hence, reinstatement is usually necessary as the next tenant is likely to have different requirements in terms of renovation or fitting out.
Also, everybody has different preferences which can mean that the existing condition where the renovation or fitting out has already done may not be what the next tenant likes or prefers to have.