I almost exclusively communicate by message/text with guests although I do check-in to ask if they need anything, have questions, (always on their first morning). My unit has a 93% review rate, 100% 5 stars, and most of my reviews are quite detailed (although they’re getting shorter after 75+ reviews).
I agree with other posters saying that you either have to 1. under-promise and over-deliver 2. provide amenities or service that give them something to write about (this costs money, although increasing your amenity budget by $3-4/visit would prob do it). It sounds like your guests aren’t so happy that they’re gushing but they are just satisfied enough to give 5 stars. How much is it worth to you to get those longer, gushy reviews?