What I heard from them is most of the money comes from a small percentage of customers doing expensive work. They don't want to take chances on unproven tools since mistakes cost too much. So, they keep using the Big 3. There's occasionally companies like Magma that show up delivering good value for a fraction of the price. Plus cheaper or better alternatives to Big 3 functionality such as Tanner. They usually get acquired, though, by companies that dislike effect of competition on profits. The integration of those features make the competition look even worse.

Those successful in EDA seem to mostly be niche players doing one job a lot better than Big 3.