It's for the same reason why people are negative about companies that require working from the office without any WFH. There are people who are established with their jobs and their teams who don't need to can just sit down at home and go. There are others who prefer the interaction and find themselves more efficient in a non-personal setting like an office.

The negativity is that many of these companies may start trending to a required work from home model as opposed to an optional/hybrid approach.

There is also a smaller worry that these companies will offload a lot of the cost to their employees (i.e. not paying for internet, space, food, etc) without compensating them for these perks that were otherwise promised/expected.