but surely there'll always be bugs to exploit?
It's about risk management. Will people be doing BYOD at GCHQ or AWE? Clearly not: the rules on what you can take in (not much) and out (rather less) are very strict. Computers which have processed that sort of stuff are physically destroyed after use, down to in some cases RAM.
But if we're talking about "the sales orders for supermarkets" or even "medical records of hundreds of individuals", the buildings are not guarded by nice men and women with guns, you aren't searched down to explaining every single item on your keyring, there is no attention paid to tempest and they don't take angle grinders to the motherboard when they scrap computers.
So if there's a narrow edge-case bug in SGX, meh, what of it? "A strong, well-resourced, well-motived attacker with formidable technical capabilities can under certain circumstances penetrate the commercial data of a large UK retailer?" So what? The staff aren't cleared, and you could get the same information by standing around outside offering free Mars Bars.
Security is about risk management, and appropriate controls for the value of the data and the capability of the threat sources, taking into account the direct and indirect cost to the business of those controls, not about spurious claims of absolute security.