First of all saying / implying that the virus is responsible for that is blatantly false , this is what manufacturers want you to believe and visibly ( sadly ) peoples are falling for it . Indeed this is not an issue where lack of stock is gouging the price , most if not all B550 ITX boards are selling for MSRP price ( in your image prices are in EUR so as per usual a tad more expensive than MSRP ) so virus has nothing to do with those prices !
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Secondly if you want to compare differences between B450 and B550 you don't compare boards from different manufacturers and different segments , especially not when you are using the most expensive B450 as an example . Here is a more a proper way of comparing things :
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As i said previously nothing can justify such a price difference .... other than greedy manufacturer behavior that is .
The strix b450i that you are using in your system got a premium of 40 € over my strix b350i from the same merchant. And the only thing that your board got over mine is one HDMI port, and and a last effort support for zen 3. That's way less than the differences between B550 and b450 itx boards. (And that was in january 2018, back when they weren't even competing with b450 that would launch in march)
I wasn't really making a direct comparison with the asus board. I mentionned the ASUS because their B550 are going to be insanely expensive probably around 300 €. Rog strix and Aorus are both premium brand, but asus had a slight lead in the itx segment because of their second m.2 slot on all their itx board, and the I/o used to be more rich. Gigabyte stepped up their game with b550, they got 2 m.2 slots as well, a backplate that the new strix won't have, and their I/O is more rich than the strix b550. That aorus board only "lose" because the strix b550 got 8 phases and a usb-c front panel connector.
The asrock board at 169€ is at what you would have considered a decent price, but it's arguably worse than the old b450 from asrock (besides the pcie 4.0) while being roughly 30€ more expensive, and it doesn't bear the name fatality or phantom gaming, so it's not even the same segment, the true replacement is going to be above 200€ as well. Asrock never had such a low end Bxx itx board before, They added a new segment just for this gen.
My point was to show that there is a general increase in price, that gigabyte isn't alone, and even when a board is sold at a "fair" price, there is a lot of compromise being made.
You could argue that those boards are not priced compared to the old b450, but rather their X570 options. Because the latter was so expensive, the former had to follow the trend. And compared to x570, well it's hard to find a reason to get a x570 board anymore, unless you actually need all those pcie lanes.