It doesn't really make sense to me. The G13 is a G-product. It should be supported by G Hub. Also, regardless of age, it's still sold and supported. Look up any "Best keypad" web page and you'll find it among the top contenders. Why wouldn't logitech include it in their new hub software? Same thing can be said about the other mice etc. that are not supported by G Hub (for whatever reason).
If I were in their shoes I would try to make it more attractive to choose a Logitech product by providing one driver software, i.e. the G Hub, for all the G-products. Not to split the products over 2 different driver softwares. Again, it doesn't make sense.