In other words, lets say I create a 100% pre-mined token and I do an ICO to sell half of it off. Why is it necessary for me to have any contact or interaction with the various cryptocurrency exchanges? I mean, once the coins are out there, if there's a market for them, won't exchanges just list them? They don't need permission or technical assistance from the developer, do they?
a couple of things here.
when you have a 100% pre mine coin which you only want to sell 50% of, people are not interested in it at all. so you will need to advertise it and the only way that works is to bribe exchanges to put it on their site so people can see and want to buy.
also there should be some place that people can buy and generally trade that coin, and for that purpose you need exchanges and they won't add random coins with no history.
and as you said they won't just add coins, the coin has to be profitable for their platform. which means it has to either pay the exchange owner or have people interested in trading it, generating volume and making the exchange some profit.