I to think its either your soil lack of nutrients or your strawbery plants past their grow by date.
There is an advantage of using raised beds for strawberies like TeeGee uses, you can move them to where you want them and as they dont take that much light and sun away you can grow short crops under them.
A lorra lorra years ago i had some like Tee Gee,s but instead of having a top on i put taut chicken wire inside the V and lined it with carpet then put the soil inside that. If i was to make them again i would use an alternative to carpet (thick black polythine holed) or just plonk the grow bags inside. Its also easier to put netting over