Morkus from Orkus
Because those numbers are not assumed. The baseline for 5e is either +2 or +3. After that, it's gravy. You can pursue the minor damage increases at the expense of better stats, or you can pursue the better mental stats and/or get feats without suffering reduced effectiveness.yeah... that annoys me too.
If the assumption of the designers is "Start with 16 attack stat increase to 18 at level 4 and 20 at level 8" then why not just build that +3/4/5 into prof?
its worse still because there is nothing about Strength that says "Can hit more accurately" by any common understanding