They don't really have much of anything worth watching, so they want you to pay at least a month and before you realize it.
I had been a subscriber for 15+ years and just canceled. I should have canceled years ago, but was too lazy. I tried for a good month to find something to watch. A few comedy specials were interesting, but none of their recent original shows or movies are even halfway decent. Most are cringe-worthy attempts with poor writing, poor acting and what appears to be a plot that didn't get any edits. Sure Stranger Things was good, but the last season was meh. It's mostly garbage originals and series from other networks that were canceled, often ending on a cliffhanger. And with all that supposed content, finding anything was nearly impossible.
I have Prime, but I never use it. Finding anything there is harder than making your own shows.