Nothing unexpexted. The PS4 Pro was a more mass-market product, launching at the same price the vanilla PS4 had three years prior while the regular model fell in price to only $299.99. But it was still ultimately servicing only a niche. The large majority of gamers still elected to either stay with their OG PS4 or to just get the standard model when coming in, saving the $100 and putting it towards wanted games or accessories.
The PS5 Pro, with its much heftier price tag, is not even designed as a mass-market product, and certainly will never be treated as one by consumers. The $699.99 price point is just beyond where the mainstream consumer is at this juncture. And then you have to add at least another $79.99 for the disc drive if you want the option to play any physical PS4 or PS5 games and other optical media. Assuming, of course, you can find one for MSRP. Good luck.
As has been said before, the PS5 Pro is only relevant for professional gamers and streamers, videophiles, and people whose income and FOMO have the magical overlap to prompt a purchase. On the proverbial Venn diagram, there just isn't a large market for it, and Sony knows this. The system exists because given Xbox's all but complete hardware collapse, the high end console market has been completely ceded to PlayStation. There aren't a lot of gamers who want a machine like the PS5 Pro, but generally speaking, those that do have plenty of cash to spend. Getting them to buy a digital only console means Sony can potentially make more income on software. And at the very least, they can sell an add-on to those who want to preserve the physical option.
The PS5 Pro is also an attractive option for those who want a high end gaming platform but can't afford to buy a high end gaming PC. The PS5 Pro will easily give a good four years of being the most powerful console until the inevitable arrival of the PS6. Given the absurd pricing of video cards currently, the PS5 Pro is certainly a viable option if you want to be future proofed for awhile and don't have the thousands to shell out for the latest cards and a beefy PC to make use of them.
For most of the market, there's the regular PS5 and sales of it don't seem to be slowing much at all. We may be about 75 million PS5s in currently, but it still feels like the generaton is only really starting.