In one line the answer is, We strictly hate overselling.
While limiting with process numbers opening the doorway of unlimited or mass number of the domain, it’s simply a bad practice along with the hosting industry. You host a lot of sites and due to the limited number of processes, all sites become too sluggish and unusable.
What’s the point of using an unusable site? So we maintain the best practice while configuring our hosting packages and avoid anything misleading to the customers.