The reason is simple: startups are made and made: the equity that should be given to you.
The general practice is to cash in 4 ~ 5 years. For example, you can cash in 25% in the first year of work, and then you can cash in 2% every month.
4. This is the protection of the startup company and the team itself. No one can guarantee that several founders will work together for 5 ~ 7 years.
What I don't want to see is that the two founders have worked hard for five years and finally made achievements.