My apologies if I misinterpreted your remarks.
You are 100% correct: MOTIVATION is the absolute key. I am certainly not special, but I do have an innate drive. Actually, it's probably closer to an addiction (which would make sense if you knew me personally). Working out indoors for me is worse than going to the dentist. It's truly painful, not only in the efforts themselves but even in the anticipation of having to do the workouts. My keys are to make sure the workouts are focused (time/intensity), short (90' or less), and consistent. One additional thing I've learned is knowing when to bail. If I get on the trainer and don't "feel" it, no sense in wasting my time half-assing the workout. Either pull the plug or simply change it up. Then commit full-speed to the next day.
I keep the workouts very simple. I've worked with a coach in the past, and I found too much complication made me want to skip. If they are basic, I can wrap my head around them and bang them out. FTP (2x20 @ 100%; 4x8 @ 105%); VO2 (4-5 x 4-5' @ 120%); Race Winners; AT (8-12 x 1' @ 150%); a few more. I'm basing the percentages off of FTP, of course. By using only a few workouts, I'm able to get through the winter without much stagnation. Hopefully, this year will be more tolerable and I can spend more time outdoors, but I have to admit there is something rewarding about the specificity of the trainer. No wasted time. No prep time, no clean-up time, no extra cash being spent on an array of cold-weather gear!! It certainly can work.
Another huge key for motivation is to have a friend. Someone who is also working out, someone to whom you must report. They can be in the house next door or halfway around the world, the important part is the accountability. The same would apply if you were working out outside, right? It's so much easier to get out there in the freezing cold with a partner than suffering by yourself. Misery certainly loves company.
Hopefully these ideas can help the OP. As for Tabatas... I certainly cannot do 40/20s! At least not with the intensity required, anyway. For me, I can do 20/10 and go full bore. I think the idea is to do what you can, but make sure they are all-out efforts. They are ridiculous. After my last Tabata workout, my comment to a friend went along the lines of: "I think Dr. Tabata probably had a hand in orchestrating the Bataan Death March." Sick bastard.
"Deserve's got nothing to do with it." William Munny