Why new iPads are only 64 gig?

All models of iPad are available with various internal storage options.

For current models:

• iPad10 - 64GB / 256GB
• iPad mini A17 Pro - 128GB / 256GB / 512GB
• iPad Air M2 - 128GB / 256GB / 512GB / 1TB
• iPad Pro M2 - 256GB/ 512GB / 1TB / 2TB

You can find the available internal storage options for both current and past models of iPad here:

https://www.apple.com/ipad/compare/?modelList=ipad-air-11-m2,ipad-mini-a17pro,ipad-10th-gen

they sell them with from 64GB to 256GB, depending on what the buyer chooses

iPad 10.9 (10th gen.) - Technical Specifications - Apple