Should other hosting providers have forums? That depends on their, and their customers’, needs.
Free hosting providers, as well as small paid hosting providers, may opt to have a forum that provides community support, as they may not be able to afford a dedicated support team to provide the assistance their clients require.
This is especially true for free hosting in which the very limited profit cannot cover the costs, something which is mentioned in InfinityFree’s Where can I get support for my account? knowledge base article, but can also apply to paid hosting providers, where a support team may exist, but cover only hosting-specific issues and not be able to assist with more general queries, like the installation of a script or troubleshooting code.
Larger hosting providers usually have a dedicated support team that can cover all of their clients’ needs, but could also opt to have a community forum if they wish to keep their customers more engaged with them and want to build a community around their name, and also save some time (and money) by having less queries that need the full attention of a support team.