The project maintainers repeatedly forget to renew their certificates, causing package upgrades to fail.
The project maintainers, in multiple past instances, have misconfigured their package manager resulting in essentially a DDoS of the AUR.
The packages are out of date vs. the upstream Arch ones, which often causes AUR packages intended for upstream Arch to break on Manjaro. Yet they consider the AUR a supported resource.
Project has had problems with mismanagement of funds in the past.
Despite all this, they seem to heavily focus on marketing, merch, and trying to sell preinstalled systems. Manjaro is in it for profit, not to make an awesome distro.