At this point, Apple could release a line of $99 drink cozies and sell out 5 minutes after they announce it. The fact that people buy what Apple sells isn't really an indication of whether the product is good or not.
I feel the same way about a lot of Apple products. The Magic Trackpad would sell out instantly if it got a new model with USB-C - but Apple knows they can ship more Lightning cables if they avoid it. It's part of the sinister math that goes into making you and I rely on Apple's constant... ahem, Innovation.
https://www.apple.com/shop/product/MK2D3AM/A/magic-trackpad-...
(I agree with you, for what it's worth - Apple is weirdly slow to update some of their products; AirPods Max stand out here as missing USB-C and the lossless audio of AirPods Pro.)
Still, it makes my relatively-new Magic Trackpad 2 feel old and alien. Whatever reason there was for Lightning is lost me when I can't juice my peripherals up with the same cable that charges my Macbook.