The fastest way to demonstrate the value of UX is to stop talking about UX.

"We need to update the website."

"That's a nice-to-have. We can't really be spending money on that right now."

"Our research showed that potential customers visit the website while shortlisting vendors. If they see that that this page breaches WCAG regulations, that's a business risk. If the hot lead sees that and decides that we're not a "serious" company, they might remove us from their consideration set and never even enter the funnel."