Its pretty simple really, exchanges profit from regular trades, and trading competition is profitable, hence they promote it.
One of the reasons behind the cryptocurrecny projects is to convince investors into storing their tokens for the future. long term investments. thereby holding the tokens and avoid trading.
That is definitely one of the reasons, that is the idea sold by upstarts and ICOs, still trying to get a foothold.
With bitcoin, regular use smis encouraged to boost adoption.