We always try to get the best possible balance between our limited resources (since we are free and we don't want to change that) and the best performance. Especially for modpacks, this is really hard to achieve. We test the modpacks in our system to ensure that they are at least starting and that basic playing is possible. Because modpacks are always a bit different and the load on our host systems is also always different we cannot guarantee anything here. But we decided to still offer modpacks on our platform because we want to offer as many options to customise your server as possible and most of the modpacks are pretty playable most of the time.