Everything needs time to develop and nothing remains same in crypto system, it is natural to have so many exchanges because all projects want to provide unique service(better quality, easier trade, more options and profit for users)that will be user friendly and adapted in most countries. For sure we will still use top ones, but if one day you discover you have so many opportunities on other dex-why not try?Every next exchange is a better version of the common used).Look to OAX and LCS for example).