An enforcement in issue. In NYC the laws are actually aggressively pro-tenant on the issue of deliberate neglect; if you don't keep the basic services working (or keep the building reasonably free of infestations, for example), the tenant can use that to delay any attempted eviction processes (justified or otherwise) quite substantially. The smarter landlords in NYC all know this, and hence generally resort to buy-outs as a tool for vacating tenants. Overt harassment-by-neglect does happen, but is quite rare.
It also reduces tenant mobility.
To some extent, it reduces mobility within the local market (and this effect can be quite significant, in some markets). But in an unregulated environment, a great many of these people simply would not be able to continue renting in the local market, at all. So it's a tradeoff, basically.
Rent control also directly causes Ellis Act evictions, IMO.
A non-sequitur; there's no reason one needs to have something like the Ellis Act in order to have rent control. NYC's market (famously) does not, for example; and profit-driven conversions of the sort you mention are generally illegal, and easily blocked in landlord-tenant court.
In other words, the Ellis Act causes Ellis Act evictions; not "rent control."