It's just that the bigger plant size and warmer weather make them use up more water and nutrients (same as soil-grown tomatoes, I think). And bigger plants have more fruit, of course!
I've never grown strawberries so I don't know how similar it is to growing tomatoes, but too much nitrogen-based fertiliser (氮肥) during the tomato's flowering/fruiting period will make it grow more leaves and less fruit (good for leaf vegetables but not for tomatoes). Normally I would maintain the same strength of hydroponic fertiliser throughout the entire growth period because there are always leaves and fruit growing at the same time. But sometimes when I want to boost fruit growth, I might increase the amount of phosphorus+potassium-based fertiliser (磷+鉀肥), although I try not to add more than 10% or 20% more than the usual amount because I don't want to burn the plant.