The exchanges are critical for price discovery. And to have open orders and a functioning order book means funds must be left there. So the 'get in and get out' strategy is rational individually, but very limiting to bitcoin overall.
Nah, funds don't NEED to be left there, that's just 'inside the the old box' thinking, in fact funds don't need to leave your wallet in order to pledge them for a current, or future transaction blockchain pros can explain the mechanics of it but it can be done
Even if you choose to do it the old fashioned way, in terms of having the funds in the exchange, any value that is not connected to an actual sale only has meaning if the position has no track record.
The exchanges are have a role in the cryptocurrency economy they also have a responsibility as well.