The processor has 24 PCIe lanes, 16 of which are reserved for the graphics card. One graphics card is therefore 16 lanes and two are divided into 2*8. So it has nothing to do with saving money, but rather with the fact that the processor does not provide more lanes.
If you really want to have 2*16 lanes, then you have to go for the Threadripper, where the processor has more PCI lanes and can therefore really provide 2*16 lanes for the graphics cards.
The tests I have read can hardly find a difference between 2*8 and 2*16 lanes.
Greetings Bert

As far as is known, with 2 graphics cards, both are always addressed with 8 lanes. However, with PCIe 4.0 8x=3.0 16x. The board makes no exceptions here, even at 700.- for a board you only get 2x 8x.