Because the valuation of equity is notional only. It may not be remotely realizable now or ever. Furthermore, it may not be possible to use it as collateral for a loan for both legal and practical reasons. Some notionally high value assets have no liquid market. It make take a decade to find a real buyer. The large majority of assets held by wealthy people are non-liquid, in the US most studies put it in the 60-70% range.

Your paycheck is denominated in cash money. It can’t go to zero or be non-liquid for years like an investable asset. That’s a rather important distinction.