I don't see how the union stuff has anything to do with Biden?
That said, the difference in CEO compensation with total salary is one of scale though - 40% increase in CEO pay is a very small absolute number compared to 40% increase in all hourly workers' pay. It would be something like an extra $5B/year in labor costs. The entire net income of the Big Three last year was only something like $12B - so that increased labor cost would reduce net income by more than 40%. Paying the executives an additional $100M doesn't come anywhere close to the same impact to the company.
So there's a balance - yes the workers should get paid more, but you don't want to basically put the companies in a position where they have zero operating margin when there is a downturn; you can't pay workers if you don't sell enough cars (and I'm not sure how much the union contract has in it to scale the workforce exactly with sales, because labor required is not just a simple constant times the number of cars sold).
Which is why historically the companies have offered bonus structures - so they can indeed give the workers a piece of the profits, without over-encumbering the companies with commitments they can't guarantee.
That said - this negotiation is the process by which the aforementioned balance is determined, so it's "working as intended" as far as that goes: the workers want more "guaranteed" income, not bonuses, as well as things like pension and health care and the like. Vacation and 4-day workweeks is also complicated; some costs (like health care) scale with number of employees, not hours worked, so shorter work weeks has a higher health care cost per hour worked (and therefore per car produced) because you need more people to maintain a given amount of production. This is countered by new cars not needing as many people to begin with. But - all these are estimates, not "guarantees", so the two sides are wrangling.
Also don't forget there's at least a third party affected by this, which doesn't have a seat at the negotiation table: people buying cars. Higher car prices reduce sales quantity (all else equal) so increasing the cost basis for vehicles is likely to reduce sales quantity. So neither the unions nor the companies know how much the labor contract will impact demand, which is ultimately the only thing that can pay for the contract, however it resolves.