How to get UX/Product a seat at the table?

As the sole product designer in my past two startups I have been an essential piece towards bringing the product to reality (user research, ux, visual design, qa). However, in both situations I found myself not sitting at the leadership table when discussing the future of the product.

Marketing, sales, support, development all had multiple employees and each department head would get a seat at the table, while I found myself on the outside looking in.

I brought this up several times (along with trying to lobby for more resources in my "departments") in 1-1 meetings with the owners but to no avail. I possibly have delusions of grandeur, but in my view if anyone should be at the table with ownership it would be the individual that is creating the experience that customers are going to pay for.

Any suggestions for how to improve/approach this situation or book recommendations that might help?