Security liabilities, most likely. Buggy decoder libraries widen the surface for exploits. And no software is bug free, nor first party vetting is free, nor san

Security liabilities, most likely. Buggy decoder libraries widen the surface for exploits. And no software is bug free, nor first party vetting is free, nor sandboxes can be blindly trusted to do their job. Better not to take any unnecessary risk, especially since browsers are already complicated enough.