17 years ago, Paul Graham was able to post this essay: http://www.paulgraham.com/wealth.html - nowadays, the compensation in tech has shifted upwards so much (https://www.levels.fyi/) - that start ups are just not competitive when you adjust for a risk premium. Finance captures this concept using metrics such as the Sharpe ratio (https://en.wikipedia.org/wiki/Sharpe_ratio) - which measures how much extra returns you are getting in exchange for the additional risk you take on. For start ups - your expected returns are lower, and the risk is very significantly higher.
Are there other great reasons to join start ups? Absolutely: several start ups are working on exceptionally cool science problems, some are solving tasks that will make a meaningful improvement in the lives of people (https://detroitwaterproject.org/, etc), some people just prefer working in a small company, you get a chance to work with your friends - but - if you are going to work for a generic SAAS company, don't accept a pay cut.
The VC that's financing your start up evaluates their investments with a spreadsheet and zero affection. Ask them how they sacrifice their own income to work on more interesting work, and they'll (politely) laugh in your face.