Which is why the club will try to take a long term view to the signings they make. I've no doubt the club could sign a DM (for example) that will improve the side in the short term but they won't make that signing if they believe it will be to the detriment of the club in the medium to long term.
Providing they can generate enough profit selling the likes of Gallagher each season then they will be able to comply with FFP. As for why Chelsea are behaving like this, there's two schools of thought. First off we have to remember that Boehly is just the face of Chelsea's ownership, the majority owner is a private equity firm that aren't in it to lose money. Either Chelsea are gambling on the fact that revenues are going to explode in the coming years and as a result transfer fees and wages will too, and Chelsea with their 100 man squad on 8 year deals will be laughing*. Or they're simply throwing as much money as needed at it to get Chelsea back into the CL on a regular basis - the hundreds of millions in losses on these transfers are insignificant compared to the potential billions in difference to the value of the club.
*I think they're a bit naive in believing that long contracts will protect him from increased wages. Undoubtedly Chelsea had a stronger bargaining position than they might have otherwise but we've seen with Palmer that if a player performs well, you're going to struggle to hold them to their original contract. And equally, if a player bombs you're going to struggle to move them on too.