Though this is not tomatoes, it is probably a similar process:
When corn is picked, the sugars begin to convert to starch. The longer you store it the more starch it has.
The next time you have sweet corn ready, try this:
Put a pot of
water on to boil,
then go pick a couple ears, shucking them as you walk back to the house.
Put them in the pot and cook. Much sweeter than any that have been in the 'fridge a few days.
The classic Italian way of drying tomatoes is "sun dried". At 150° you are probably 'cooking' the sugar into starch.
Even
solar driers can get too warm for good tomatoes if it is hot weather.