ANS: Money
Expensive tube preamp, compressor, noise gate, FX processor, parametric EQ, and a Ham radio if you must know.
Doesn't mean you can't get 90% of what they do at a fraction of the cost. I do it every day and I didn't spend that much. If you don't know how to use use sound gear; then concentrate on making what you have work to its fullest. For one - don't over-compensate the use of the bass/treble controls on the mixer. If the radio has a narrow TX bandwidth - it won't make a real difference. But you have probably noticed this by now.
Like I told you a while back, they don't use mixers for one. They use a dedicated mic preamp.
The REAL secret in a hifi TX is having a radio that can TX wide to begin with. There are more shops all of time catering mods to customers for broadbanding the RX - not so much for TX. But most CB's TX filters will go as wide as 3.3khz with the standard 2.8khz filters. Just because any filter really doesn't shut off until a certain point beyond 2.8khz.
I have that 'bass master' sound using a radio that has 4.0khz wide TX radio, a mic preamp, and a condenser mic much like you have now. If you change the X bandwidth of your radio, that will have the most positive change.
Is there a difference between a dedicated mic preamp and a mixer? Yes; the dedicated preamp are a higher grade pf preamp. You are paying for things you don't need in the mixer and get a preamp that is doing what it does best - concentrating on clean audio for a single mic.
Congrats on making it work.
Bet you feel a bit of satisfaction from DIY . . .