I've written many 48 hour games. I've also written games that drag on for months or longer without apparent progress.
The difference literally comes down to whether you are doing easy things or not. Having an engine or framework does help make a variety of things easy, but it does nothing for the one or two features that aren't. Eventually you hit a wall where it takes forever, and that's your next month. You get over the wall and then a flood of other new features come in almost instantly. Also in the same ballpark are features that you have coded before and are familiar with, vs. ones you aren't. You can get a lot done "from scratch" by spamming preexisting knowledge at the problem, but it still takes time and it isn't exactly easy either.
Last of all, at first clone-and-modify is enough to feel interesting. So you go very quickly, because you care little about the result. But after a few dozen times doing that, you're done, and you want to expand the parts you care about. That creates more barriers to get over, more months where progress is slow because your ambition is big enough to no longer follow the easy path. More months where problems are on the content development side, not the runtime. That part is always difficult. Scope is deceptive.
The difference literally comes down to whether you are doing easy things or not. Having an engine or framework does help make a variety of things easy, but it does nothing for the one or two features that aren't. Eventually you hit a wall where it takes forever, and that's your next month. You get over the wall and then a flood of other new features come in almost instantly. Also in the same ballpark are features that you have coded before and are familiar with, vs. ones you aren't. You can get a lot done "from scratch" by spamming preexisting knowledge at the problem, but it still takes time and it isn't exactly easy either.
Last of all, at first clone-and-modify is enough to feel interesting. So you go very quickly, because you care little about the result. But after a few dozen times doing that, you're done, and you want to expand the parts you care about. That creates more barriers to get over, more months where progress is slow because your ambition is big enough to no longer follow the easy path. More months where problems are on the content development side, not the runtime. That part is always difficult. Scope is deceptive.