If you are a startup, courting a large customer can compromise the integrity of your project. You have no leverage at all, which means the product will start to look like what they want it to be.

And because you made a deal with them when you had no leverage, the terms will also be awful, and difficult to renegotiate. So you have to go try to increase margins off of smaller customers, all with a product that looks like what the person you aren't making money off of wanted it to look like.

Hypothetically speaking, of course. Because I definitely for sure did not work for a place who tried to go big too soon and ended up with a modest exit.