I was looking through my games and noticed that I have a few with well over 90% completion but not finished, an example is GOW where I have done everything but defeat the Chief Valkyrie another is Persona 4 golden where getting the last Fish stopped me I ignored it and completed the game knowing that if I went back it would only be to get the plat , now some games  don't worry me because I either completed the game story wise or was never interested in doing a 100% anyway but the ones that have me in two minds are the ones that I gave up on due to the frustration of getting so close but at the same time sick of repeating them , what about you guys?.

Final Fantasy VIII and IX. Played both a lot and enjoyed them even, but still didn't finish them. I don't know, suddenly I just lost the motivation. I only finished both years later. I can't explain that myself, either.

I've hit a road block in Farcry 5, I've had it since April 3rd, but i'm just too lazy to do Jacob's region (My last one out of the 3 main regions). Jacob is just such a boring villian who isn't worth the last ten hours it will take the complete the region.
I'm also heavily invested into Rainbow Six and work very odd hours, so I just can't make time to play a part of the game I won't even enjoy.

I've experienced that too. It's a weird feeling, knowing you're like at the very end of the game but can't push yourself to finish them. I know I've literally loaded save files in RPGs year later after leaving them, only to play them for 20 minutes, beat the final boss and then actually be done with the game. I can't give an explanation either, other than maybe getting like very burned from the game and it unfortunately hits at the very end?

I understand with GOW. The final Valkryie is a son of a bitch to beat lol,. Still a great fight though and it's VERY SATISFYING ripping her wings off.

FFXIII. Despite how much hate I give it, I do give all FFs that I own a good try. Unfortunately, once I got to the final boss, I couldn't do it. I thought to myself "why am I still playing this game when I can play a better game?"

Far Cry 4 and other similar Ubisoft games like Assassins Creed I could never really get into despite liking set pieces and foreign environments.

I can't even count how many. But the ones that spring to mind are these. I had 2 playthroughs of FFXIII totalling over 150h but I could never get the plat because I couldn't beat the last mob. I never actually finished GOW3 because I got too frustrated in the fight against Zeus. I quit, watched a video of the fight and ending cutscene and called it a day. I burned out on ACO because it was just too big. I think I was about 70% through.

My most notable game that I could never even come close to finish is Kingdoms of Amalur. I played it on 3 different occasions over the years for about 50h each but I could never get past half of the game because I burned out before it. I really like the game but there is just too much loot and quests.

I prefer multiplayer games so I never have the motivation to complete the majority of single player games I've played.

Rarely but just had this problem with Persona 5. The last 'day' lasts forever and I even got to the final boss and tried to beat it. I just am not strong enough, so in reality I just need to farm and level up a bit in the area I am.... I just didn't. I've started playing other games again.

Some japanese games require crazy grinding at the end that's not worth my time and effort so I just watch the endings on youtube.