Also, we can bypass this kind of thing and did up until the last century. Further, certain couples bypass this type of thing all the time routinely. You don't see gay male couples giving each other diamond engagement rings and yet their marriages aren't exploding in spectacular fashion.
It doesn't even make sense from a financial penalty standpoint. Anyone who is on an upward trajectory would be able to bounce back from losing a month or two of salary relatively quickly in which case it's not really forcing long term commitment.
There is no real point to this ritual other than showing off. The guy gets to show off how much cash he has and the woman gets to show off to everyone else that she has a guy with a lot of financial resources. It is completely arbitrary and we have arbitrarily converged on a diamond as a mechanism to do this. Sure giving rings makes people feel good; receiving and gifting any present makes people feel good; but it's absolutely not a necessary requirement for a healthy relationship.