I am very confident that I know what the issue is here, and that it's not really WZ's fault. Sometime ago browsers started being a lot more aggressive with blocking autoplaying sounds, with the aim being to prevent ads from playing sounds. For most browsers the default is to block sounds before the user has interacted with the page.
As a user you could
a) Click around when the page opens to "interact" with it, which should work.
b) Change the browser settings ( should be the same as for Lichess basically :
https://lichess.org/faq#autoplay )
c) When you have used a site many times, the browser might "trust" it.
What Fizzer could do is show an icon when sounds are blocked and/or make an FAQ that informs users about it. Since very few will know about the browser settings. The reason it might work on other games is that a) they don't use a new page when starting a game b) they have a play button that you have to click, which might count as an interaction ( depending on browser).