The issue with this is the scenario where either company deviates from the status quo. For example, company A decides to make a tradeoff: invest more into R&D at the expense of sales and marketing. If Company B remains the same, company A may suffer a temporary dip in sales, but in exchange, their product becomes better over time and they are able to take more than the original 50% of the market due to having a superior product.
What you're talking about really only works if both companies agree to stay stagnant and collude to keep the status quo as-is. To be fair to your point, this has happened a few times historically, but it is usually considered price fixing and is very illegal[0].
What you're talking about really only works if both companies agree to stay stagnant and collude to keep the status quo as-is. To be fair to your point, this has happened a few times historically, but it is usually considered price fixing and is very illegal[0].
[0]: https://en.wikipedia.org/wiki/Price_fixing#United_States