Have any of the managers/developers been confronted on their complacency, and if not, why? Sadly, you can't just fire someone without first giving them a chance to turn things around. Nothing motivates better than fear, but it can also cause people to become resentful towards the company.
You need to pull each employee aside, especially the manager(s) who should be ensuring efficiency is kept at acceptable levels. This sounds like a double-edged problem. Employees not realising they're dropping in efficiency and managers not noticing the drop in performance and also failing to do anything about it if they have noticed. Sounds very much like a safety in numbers scenario at the moment.
All you need to say is, "Hey, we've noticed you're not performing as well as you have in the past. Is there a problem we are not aware about, is there anything preventing you from doing your job properly? Lack of resources, lack of proper tools, personal issues? Are you being asked to do too much, is the work too difficult and is there anything we can do better to make it easier for you to do your job?" but at no point should you start pointing fingers and placing blame upon people. Talk to your employees like you would your best friend, only more professionally.
Free food and a great environment shouldn't be the only motivators the company offers by the way. It's like those code hackathons that offer free pizza, beer and cans of Red Bull, just because you're giving away free stuff, doesn't mean you are entitled to overwork or unreasonably expect more from your employees or those around you. If the work isn't stimulating or challenging people will grow bored as well, there is usually more than one answer to a problem. Are unreasonable time frames and expectations being placed upon your employees? If you're asking for things to be done within 2 weeks, but it should be a 3 week job, who is to blame? The business imposing unreasonable time frames or the employees who have to try and get the work done within said time frame?
The fact you're saying it's a twelve person team and it's the whole team to me signals it is a management problem. Solve the problem at the top and you'll most likely notice the trickle down effects to the rest of the team.