User blog comment:WhiteFilipina/Why did Monster High create a new timeline?/@comment-27323068-20180807030858

Many franchises go through reboots mainly to attract a newer audience. The reboot has a lot more bright and friendly colors compared to the original most likely to catch younger kid's eyes.

There was also an article I read a while ago (which I unfortunately can not find at the moment) that talked about how the original MH was getting a bit bland story wise. It mainly talked about how many characters were seen for one special and only had one doll and were never talked about or heard from again which made things confusing as well.