There are many reasons for ICOs to collapse in 2019. But I think the regulatory barrier to token sales is the biggest problem that causes ICOs to die. unsold, limited deals and lots of other reasons are also quite important.
The real reason is discussed in this thread already, it is not because of the regulatory barrier, if you check the market you will see projects coming out every month but the issue is always the huge amount of scams we saw in the past few years and it is hard to trust any project and majority of the projects that collected millions did not fulfill anything and with that in mind who will be trusting any ICO project.