I have noticed the same thing about indoors and outdoors. The trainer is really a more measured effort, no headwind, tailwind or crosswind, no uphills, no downhills, no corners, no stops, nobody to chase down or keep up with, all zones reached on pure willpower with no distractions. Keep at it, you will have good days and bad days, good weeks and bad weeks. Make sure that you include rest days on the trainer just as you would outside and make every fourth week a light week after progressively increasing your efforts in the previous weeks. Within a given week, efforts should also be progressive and include at least one light or rest day on the cycle. A ride on the trainer at goal Heart Rates is equivalent to a ride and a half outside.