Where have my shrimp gone?

I’ve had this 7.5 gallon cube for about 6 months. Stocked with a Betta and a few ottos. 2 months ago, I put in 8 yellow goldenback shrimps. After about a week, I stopped seeing my shrimp. I have not seen any dead shrimp and my Betta took 0 interest in them so I doubt he ate them because I feel like I would’ve seen shrimp scraps if he did. I saw a shrimp about 3 weeks ago and another one about a week ago, but no sightings besides that. Do you think they’ve mostly died off or are masters at hiding? The piece of driftwood is pretty large for the tank and has lots of holes, but I feel like I would see my shrimps a little bit more given there’s 8 of them.