Oh, that's awesome! And it's so reasonable to hit a roadblock at the 50% mark! I do every time, and it's almost always because I've put so much effort in that I start worrying that maybe it wasn't worth it—maybe I should just give up. It's hard to push through the second half of a draft.

Another reason why a lot of folks stall at the halfway point is colloquially called the "muddled middle"—where writers have a clear image of how a book starts and a relatively clear idea of where they want it to go, but not as many ideas for how exactly it gets there/how to keep it exciting during the looooooooong stretch between beginning and end. There are a lot of ways to combat that feeling, but it can definitely be rough.

It is absolutely not because you're lazy! (That's very clear from your dedication to prepping and your amazing progress in NaNo.) It's just that writing books is hard, and there are so many unexpected roadblocks along the path. If you ever decide to come back to a draft and finish it, you'll have a bunch of options to choose from, and I think that's amazing. You don't have to finish any of those books now.

I wrote the first half of one of my projects in 2014 (during NaNo, actually!) and then stalled at the middle and worried that it was all nonsense and I shouldn't continue. I let that half-draft sit for over six years before I speed-wrote the second half in June/July of 2020! So it's never too late to finish a book.