Because the power is disproportionally concentrated with one party - the service provider. The users of the service are numerous, comparatively small and uncoordinated.
In a situation like that, users have no means of resisting egregious terms, and no you cannot pull up stuff like "if you don't like it, don't buy it". As I wrote, the users are uncoordinated, and would take a huge effort to coordinate. Boycotting services rarely works (if ever). So what we end up with is that legal teams employed by firms optimize to shove as much bullshit into ToS as they can, the users grind their teeth and bear the bullshit, and get shittier service. Nobody really wins, because I'd argue the marginal gain for the company is minimal at best from this.
The government is not there just to enforce laws, but also to legislate such that the scales are balanced. Otherwise we may as well live in a dictatorship.
But some terms were claimed to be reasonable. If power being disproportionate is sufficient to void terms, why not those terms too?
> The government is not there just to enforce laws, but also to legislate such that the scales are balanced. Otherwise we may as well live in a dictatorship.
Should the state just prohibit all agreements between two parties unless the state's adjudicator decides they are exactly equal in "power" and permits it? Sounds horrific, like a dictatorship. The government is not my guardian and does not do my thinking for me. I get that many people are subservient and would much prefer that, but that's no good either. There's an enormous middle ground between anarchy and "the state intervenes to allegedly 'balance the scales' in every aspect of peoples' private lives".