The product grows more and more elaborate, and more and more expensive, but the expense is offset by cheap credit provided by sellers eager to encourage buyers to buy.
Buyers see that everyone else is taking on mounds of debt, and so are more comfortable when they do so themselves; besides, for a generation, the value of what they're buying has gone up steadily. What could go wrong? Everything continues smoothly until, at some point, it doesn't.
Yes, this sounds like the housing bubble, but I'm afraid it's also sounding a lot like a still-inflating higher education bubble.