Why isn't my new iPad (10th generation) compatible with the 2nd generation Apple Pencil?

The iPad 10 fundamentally lacks the necessary hardware. In more detail...

The iPad 10 lacks the magnetic/inductive dock found in many other models of iPad. As the second generation Apple Pencil lacks any means by which to connect, charge and pair using a charging cable, the second generation Pencil (and similar Apple Pencil Pro) is not supported by your iPad 10.

Here is Apple's definitive compatibility list for Apple Pencil and iPad:

Apple Pencil compatibility - Apple Support

Different iPad models support different Apple Pencils - the host iPads having different internal hardware. Inductive charging, as used by the second generation Apple Pencil and Apple Pencil Pro, is currently the preserve of the more expensive models of iPad.