Along with the possibilities that people have raised: Too much too soon, inflated FTP, maybe VO2max is lower % of FTP for you, too much non-training stress, plus “Build” is hard (so to execute each workout as prescribed you will need to be more prepared nutrtion and rest-wise than you did during SSB). But, lack of motivation is often a sure sign that you’re in a deep dark hole.
But one thing to consider, on the mental side, it is not just about “wanting it more” or whatever people might say. Rather, i think that indoor training in particular might lead people to a sort of rigidity of thinking that is actually counterproductive.
Like for example, if you’re riding outside your effort level naturally scales. If you’re going to do intervals up a hill and you find power dropping off towards the end of the final intervals, you might not even really notice. If you looked at power file later, you might think oh, i could have executed that a bit better by going out easy, but you would never consider it a “failure,” as you clearly got enough time at the right intensity to tax yourself. Job well done, you’d say! But on the trainer, especially with erg mode converting what really is a range into a single target, that same scenario means death spiral and people think of it as failure. Really, it’s perfectly acceptable to lower the intensity and gut it out.
Similarly the plan itself is only semi-tailored for you. If a workout says do 20 mins worth of Vo2max intervals, that is just a guess at an amount that will tax you and drive adaptation. If you hit your power targets, hit em again, again and then start to really drop off after, say, 15 minutes, guess what? You just executed a vo2max workout, exactly the right amount of it, and the proof is in the pudding in the fact taht you couldn’t do anymore and next time you try to go longer. But again, on the trainer, in erg mode with the resulting death spiral, people view that as failure.
So like yeah you have to toughen yourself but also be reasonable