There are two arguments here: technical and economical.
Technically, the A320 *chipset* should be able to run Zen2 just fine, BUT, the *implementation* of it on the board maybe the limiting factor; the board is not robust enough to run it stably long term. (layers, power delivery, unknown corners cut to be *good enough*)
Economically, the board mfg has no interest in making the "cheapest" board a desirable option, and lose out on money by forcing an upgrade at either initial purchase OR upgrade time down the road.
So, if your reality is different than ours in the USA, just explain the economics behind it.
There is no shame in sharing how the rest of the enthusiasts with limited options have fun with what they can get.
BUT, not sharing the whole picture leads to frustration about why something is an issue.
Its hard to explain the economics behind it when the prices changes every day, but ill try. The minimum salary is $12500 at current rate that is u$s272, but remember this changes all the time and tech prices are valued in dollars.
The cheapest B450 is the Gigabyte B450M-DS3H at $4200, that today is around u$s91, and this board is really not that good, with just 4+3 is no better than a A320 at power delivery. This is also the case for most cheap B450 boards.
The Asus A320M-K and Gigabyte A320-S2H are $3200, that is u$s70, both of them are 4+2.
Now this is the problem, a 120GB SSD is $1000 (u$s22), and 4GB DDR4-2666 is $1150 (u$s25), so most people when buying online are faced with the option of a B450 with OC, or a A320 with a SSD or 4GB more RAM, most go for that option, and if i had to build a PC for someone else that has no idea of what OC is i would do the same.
In the end, a very BASIC PC like a 2200G + 1TB HDD + 2x4+ A320 + horrible psu and case is around $17000 -> u$s370, and im talking about BARE MINIMUM here... the case dosent even have USB 3, so you can see why upgrading motherboard is not a priority here.
So the options end up to be
2200G + 1TB HDD + 2x4+ A320 + horrible psu and case u$s370 <- 2nd popular
2200G + 240GB SDD + 2x4+ A320 + horrible psu and case u$s370
2200G + 240GB SDD + 12GB+ A320 + horrible psu and case u$s394 <-Popular
2200G + 1TB HDD + 120GB SSD 2x4+ A320 + horrible psu and case u$s393 <- 3er popular
2200G + 1TB HDD + 2x4+ B450 + horrible psu and case u$s391
2200G + 240GB SDD + 2x4+ B450 + horrible psu and case u$s391
2200G + 240GB SDD + 12GB+ B450 + horrible psu and case u$s415
2200G + 1TB HDD + 120GB SSD 2x4+ B450 + horrible psu and case u$s414
etc more options with better cases and PSUs but that goes way up. But ask yourself, the averange joe does OC? The anskwer is no, this is why they tend to go for what is cheaper, and A320 is really feature rich. And the 2200G and 2400G is the case were B450 matter the most, this is why i choose this case, ocing the IGP makes all the diference in those budget builds, but when you start going to cases were you have a 2200G + 1050, or a 2600 + 1050/RX570/1060 B450 matters a A LOT LESS, because A320 is just fine to drive such CPUs at high turbos, you loss 50 to 100mhz MAX due to lower XFR.
Im not going to sum all the the components now, but a 2600 +8GB+1TB+RX570+B450 cost the same money as a 2600 +8GB+1TB+120GB SSD+RX570+A320 or 2600 +12GB+1TB+RX570+A320... and the A320 options perform better either due to more ram or the SSD.
BTW dual channel is enabled at 12GB ram, it performs a little slower than 1:1 dual channel, but is way better than single channel.
Personally i care about the technical reasons and the promise that was made, the economical reason, while VALID as a argument, is not valid as a justification. But we should stop this now, no point in keep arguing this until we have the full picture. For example what happens with A320, they stop production? they launch A320 V2? they are going to discontinue it? New chipset? And now many B and X boards dont get the updates.