Their thrive on old habits, and it seems unlikely they'd care unless pieces like these are shared a lot and their target audience starts caring (and leaving). For a casual WA user, if WhatsApp, their default application is slow, then their PC is slow. Not to say that Meta could've easily uprooted what software development power it had before Covid and that WhatsApp dev team is just incapable of creating something new and slick or at least make their Electron wrapper app comparable to others' in performance.