Maybe you should try mixing so you have a better understanding of why such choices are made. I can assure you building a good live mix is not as easy as most people think it is, and getting a good bass sound is often difficult if not impossible.
I am guilty myself, of mixing the bass light in the mix. The reason is because I personally think there are other more important priorities, and if I can't make the bass sound nice without it covering up the vocals and melody, it gets turned down or thinned out. On top of that, often there is so much bass coming from the stage that it overpowers the rest of the mix even if I push the bass channel fader all the way down.
This is not always because the bass amp is too loud. Often the problem is compounded because everyone wants a bunch of bass in their personal monitor. Unfortunately when the bass is spilling off stage at different phase angles, from so many different directions, it just make a hopeless muddy mess, and the only thing that I can do to clean it up is the pump the room with so much SPL that it would have everyone running for cover.
Back to my priorities. Keeping the volume at a reasonable level is very high on my list. So if the musicians produce so much stage volume that I can't create a nice mix at a reasonable volume for the audience, I will create a crappy mix at a reasonable volume....or as close to reasonable as I can make it. It will be the best mix I can do at that SPL though.
Then again, and to be totally fair, a lot of it comes down to personal taste. So if the audio tech does not know your band and understand its sound concept, your going to get stuck with whatever the audio tech thinks you should sound like. I personally think if you could have everyone in your band create their idea of an ideal mix, you would probably be surprised by how little consensus there is even within your own group.
As far as the conundrum of mic'ing bass amps versus guitar amps. The same problems are encountered anytime you mic an amp, but typically with guitar you can get a really great tone out of a mic'ed guitar amp. As I said earlier, IMHO it can be next to impossible to get a decent bass sound live, and using a mic can compound the problem. However, my personal opinion is that I would rather mic a cab than use a Post DI off the back of an amp. In fact, post DI is my absolute least preferred option
, and yet many bassist are adamant that they have to use Post DI, and swear it's the best thing since sliced bread
. For the record, I used to think this way too, before I became an audio tech.
Continuation of mic'ing discussion. Modelling is becoming more and more common, and many guitarist are running modeling rigs and IEMs with no amps. So back in the day, it was pretty hard to get a good guitar sound without using a mic, but that's changing.
Actually I don't think it was all that difficult back in the day. I assembled an ampless IEM rig back in 1995 and we used the top of the line Digitech rack mount guitar processor. I believe it was something like a GSP2101 LE with a pair of 12AX7s in it. It was a pain dialing in the patches but the guitarist got it sounding pretty decent. The only criticism I ever heard was we sounded too much like a CD. Some people prefer the sound to be nasty and obnoxiously loud
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If the player is going for a clean sound my preference is to have the DI between the bass and the amp. I.E. take the amp totally out of the signal path. This gives me the cleanest most unprocessed signal possible, and also means the bassist is free to adjust his/her amp without impacting/degrading any of the mixes I control. If you use a pedal board for effects, it should go before the DI...and if you think it's important, the end of the pedal board is where I would recommend inserting a speaker sim like the ones I suggested earlier.
