I always see the argument of "when all the mom & pop landlords are gone, major corporations will own everything, so we have to protect them".

That consolidation is going to happen anyways. It's inevitable. The only factor is how long it takes for it to happen, and how big the payout will be for small landlords when they finally decide to cash out. There's much more at stake for the renters.

Forcing small landlords into choosing between selling immediately or facing bankruptcy in the near future is morally preferable to putting the burden on renters. The world isn't really a worse place if a landlord has to liquidate their assets at a 150% net profit now instead of 320% in ten years (after accounting for all rent collected and taxes paid).

If they had the capital to afford a commercial property in the first place, this won't be potentially life-ruining. You can't assume the same for a non-chain restaurant or grocer that serves as the owner's livelihood.