This is a common pattern for new bug classes. Nobody thought to look at this, and when they did, the rabbit hole went deep. We likely haven’t seen the bottom.
AMD are not better. They’re probably worse. They’ll be looked at when the Intel tree stops bearing fruit. But finding an Intel bug is higher impact, so that’s what researchers want to look at.
Intel and AMD don't have to share the same bugs for AMD to be worse.
Consider you've got two sets of vulnerabilities: [1, 2, 3] and [2, 4, 5, 6, 7, 8].
If I label set 1 Intel, and set 2 AMD, then you can see how doing your research on Intel first will make it seem like Intel has 3x the vulnerabilities as AMD - even though it actually has half.
AMD are not better. They’re probably worse. They’ll be looked at when the Intel tree stops bearing fruit. But finding an Intel bug is higher impact, so that’s what researchers want to look at.