Figma's valuation is a fragment of that of Adobe. Saying most designers use Figma is as distorted as saying most designers use macOS, even if both things may be true in a specific niche (e.g. tech companies in the US).

In my experience of the rise of macOS among developers, the biggest driving force was mobile app development and mobile web development because Apple refused to provide first party developer tools or emulators usable on other operating systems and made it intentionally difficult to run macOS on non-Apple hardware or in a VM. Previously macOS was largely associated with designers, not developers. This move also started blurring the lines more with designers making the move to development and (to a smaller degree) vice versa.