Internet forums have existed for a long time, and for an equivalent period their moderation policies sufficed. If you disagreed with one forum, there were plenty others to take its place.
However, we've now approached a reality in which these forums have dwindled or become centralized. A much larger audience participates, and these forums have now expanded to be parts of multimedia service conglomerate megacorporations. There are no other choices, and these organizations are spread into aspects of life that would cause being banned to be quite inconvenient.
For example, getting your Google account banned could in theory result in loss of access to most of everything here: https://about.google/intl/ALL_us/products/. It gets worse when you consider that google could be your internet provider. And of course google insists everything be forced through their accounts. Loss of access to your account could mean loss of access to the internet. Hell, you'd lose access to your god damn Nest thermostat.