Oh I have no doubt they can get at least a skeletal framework of a proper gameplay loop up at some point. Point is, that still doesn't really exist, and so the idea that people are only spending money now based purely on what currently exists and nothing more, is quite clearly not true.
And should the money keep rolling in, it gives CIG leeway to continue to develop slowly, only incrementally adding on to such a skeletal framework over years instead of making it max priority, helping them kick the 'dream' can down the road ever more. "Dont worry everybody, I know it's not currently what was promised, but I assure you, be patient and it will come in time! In the meantime, here's what our guys in Frankfurt have been working on for the past year - ultra realistic interactions between oil and water on the ground, creating slippery surfaces!".
EDIT: Also, there was a time when Roberts said they were gonna stop adding items to the feature list for PU until they got it all done. That would have been the right move(though the feature list even at that time had already bloated to a ridiculous level), but Roberts is Roberts and simply cant help himself.