after some more digging it seems it's because the default pngs are not present in the respective thebezelproject game overlay folders. And the default system png for eg. snes.png doesn't get called when you select "thebezelproject" as deco and since the Super-Nintendo-Entertainment-System.png is nowhere, the rom won't launch if there is no bezel.
Also, the default.info and default.png in the root (thebezelproject/) are 1KB and the png is an unknown file format and the .info has this info:
<DOCTYPE html>
<html>
<head>
<meta charset="UTF-8"/>
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Error 404</title>
<!-- Stylesheets -->
<link rel="stylesheet" href="{FOLDERNAME}/theme/style.css" />
</head>
<body class="fadeDown">
<center>
<h1>Error.</h1>
<div class="errorCode">404
</div>
<p>I can't find what you are looking for...</p>
</center>
</body>
</html>