Feels like this sums up so much of our world, it's scary. Anyway.
Main issue is with "mutual consent", or more specifically, negotiating power.
A contract negotiated between two parties with similar amounts of power will have terms that protect both sides. These will often define things like advance notice for cancellation, or penalties for early cancellation. The paying party usually wants the most flexibility for cancellation, the counterparty wants certainty of revenue, so a balance is found. Assuming everyone did their work, both sides should be reasonably happy with the terms of the contract.
A negotiation between a large corporation and an individual (low-level) employee is not really a negotiation, the individual employee can only accept or reject the corporation's offer but they cannot typically negotiate specific parts of the contract. Individually, they have no leverage. If they decline the offer and move on to the next company, they don't have any more negotiating power over there either.
Let's also talk about BATNA a bit here. BATNA for a company: they just hire the next person that comes along, still with the terms dictated by the company. BATNA for an employee: accept an offer somewhere else (again with the terms dictated by the company), or starve.
So what can an individual employee do to get more leverage and get an outcome closer to a "mutual consent" contract? Well, the obvious option is to coordinate their negotiation with others who also have low individual negotiating power but share similar interests. Combined, they should have a lot more leverage.
We could call this negotiating process "collective bargaining", and the group of individuals a "union".