I experienced the same with my kids. Over the years, I purchased Bloxels, LittleBits, Lego EV3 and many other random tech toys. Unfortunately, the novelty wears off and they see little usage without parent intervention. Over the past decade, only the "big box of random Legos" is consistently used.

I find persistence is a big problem with most tech toys. For example, if kids invest a lot of time building and coding an EV3 robot, they never want to take it apart and start over. Once you finally disassemble the project, it takes a while for them to gain interest again. Although Lego Technics and EV3 have a steeper learning curve, they're still great toys and both kids and parents really do learn a lot. However, the simplicity and creative possibilities of basic Lego bricks appeal to kids for many years. Legos, by far, have the highest "return on toy investment" in our house :).