Does anyone know why iPads don't work with CarPlay?

Perhaps consider that iPad and iPhone have, to some degree, different features and capabilities - some being unique to the individual platform. iPhone and iPad are not necessarily interchangeable.

CarPlay is only one of the features that is exclusive to iOS for iPhone.

Apple do invite constructive feedback and comment via their product feedback pages:

Product Feedback - Apple

iPad and iPhone are similar - but also functionally different in many areas.

Apple’s product development, positioning and strategy is known only to Apple. We cannot speculate as to Apple’s motives or intent; the Terms of Use that govern participation within these Support Communities disallow speculative comment.

If you have views that you wish to express to Apple, the product feedback pages (link already provided) are the most appropriate channel to voice your opinion.

Thank you for the link. I definitely let Apple Support know my displeasure with their choice to exclude aging people (with limited eyesight) from using iPad with their CarPlay systems to display maps along with the verbal directions. Currently, I only get verbal directions in connecting my iPad to CarPlay (via Bluetooth lightening connector) and must mount my iPad on my dash to see the map to anticipate turns, etc. Thank goodness Velcro works very well in holding my iPad in place.

They were never even designed to use it.

When an iPad fits in your front pocket maybe things will change.

Send them feedback.

It appears Apple designed the CarPlay system for people who do not have limited eyesight and rely on the larger screen iPad.

Shame on Apple!