People support it because of the polish and the commitment that the Dev has put into its previous iteration. No one has said that it was going to be FOSS or non-monetized. From day one everyone knew that Sync was going to be a port to Lemmy with all strings attached like it was before.
There is also the initial load problem where it would take longer to load in Firefox compared to chrome. Yet people will attribute it to the browser and not the fact that assets were already stored in chrome.