The 335i coupe already competes with and owns the G37 and A5. The M3 coupe competes with and again owns the S5.
The new E coupe is bigger and a new style, BMW does not need to compete with that car, with the coupes they have available already sell a heck of a lot more than benz.
While people would love a 5 coupe, it doesn't make sense, the 6 is the 5 coupe.
A5 competes directly with the 3-series coupe. It's the reason Audi built it in the first place. It's sorta based on what E90 could have been if BMW ditched Bangle... In fact, some people go as far as to say that, today, "the closest thing to a real new BMW today is an Audi A5 (RIP, thx a lot Chris!)".