Well from my personal experience at startups quite a few of them do give bonuses. Its a way for them to have control over whether you get part of your compensation. Often based on performance (for the reputable ones) but sometimes just based on whether they feel like paying it!

The bonus isn't anywhere near what the larger tech companies do. I get it, they are cash strapped, my perspective is that they should go back to the VCs and double the size of their investment rounds to accommodate bonuses that are nearer to upwards of 50%-100% of the base salary. And the boards (which also include the VCs) shouldn't be balking at the idea of having employee equity pools greater than 5%.

They are acting like they are doing you a favor, but the current reality is based on greed (from the board) and it will simply take a collective of engineers to simultaneously realize they are undervalued, just like some financial professionals realized in the 80s.