Modern motorcycles are way, way safer than an early 80's CB750. ABS, traction control, brakes and tires that are light years ahead of 80's tech, lighter weight, more agile etc. The only reason to ride a CB750 is because they're cool, not safer!
1. As 'more modern' bikes are lighter, have better brakes, suspension/handling and most importantly ABS.
2. Harley can't move on with the times. They did with their 'V-Rod' featuring a 'modern' liquid cooled engine designed by Porsche. They discontinued it this year. Harley riders want the old Harley image.
They're trying to pivot into new markets as their customer base is becoming too old to ride or simply dying off. https://www.harley-davidson.com/us/en/motorcycles/future-veh...
They are incredible fun but unquestionably dangerous.
I, for one, have refused to purchase a sport bike on numerous occasions - including my "dream bike" - because I know its too much bike and that might get me into trouble. I've never felt that way about any of my cruisers or dirt bikes.
If I go modern I'll probably get something like an SV650.
It's more the ability to ride long distances comfortably I want not pant wetting speed.
Or maybe they are self aware. Realistically only a very small share of the people who are riding a 100+hp bike can really handle that power.
The biggest transformation of bikes the last 20 years has been handling. Now they generally all handle pretty well, with a few exceptions. So if you like the style of early CBs and Zs, pick one of the many retro remakes that have come out in the last 10 or so years.
For small displacement bikes that are light, inexpensive, and reliable, you could consider the Honda CB300F, which is available with ABS and a modern 300cc engine. If you must have a slightly more retro style, there's the Suzuki TU250X - it's a solid all-around bike, but no ABS.
Both will likely be just as fast as the older CB750, handle better, stop better, and probably not cost much more money (CBs have gone way up in value, plus whatever time you spend brining it back to reliable condition).
If you want a mid-displacement bike, yeah, they're fast, a bit more money, but still better bikes in just about every way compared to anything form the 70s.