What the FOH guy *probably* understands you to be saying is something like this: "Send a copy of the main mix, minus the bass and drum stems, to my stage wedge."
On some boards, that's easy. But he probably has an objection:
1. If he sends your wedge the main FOH mix (minus bass and drums), where you stand on stage won't sound anything like what the punters are hearing in the middle of the room.
2. Even if he wanted to simply oblige the letter of your request, perhaps he's on an older analog board and feeding stage wedges from aux outputs, not mains. The way many analog boards are rigged for duty, you can't simply assign the main mix back to an aux, and it would be even more of a problem to tap the main mix minus certain instruments for an aux mix. (That is, almost any decent board is capable of what you were asking, but on the gig the capabilities to route the whole mix or a sub mix are already spoken for.)
3. He might have been unwilling to add more than was necessary to the stage sound. Many FOH engineers work to minimize the stage volume and spill. If the bassist's wedge is between the guitarist's Fender Twin and the lead vocalist's wedge, I'd be reluctant to send even more guitar to the bassist's area of the stage just b/c I have the Twin's amp mic in the FOH mix. I'd also hesitate to feed vocal effects to a hot stage wedge, and I'd want to keep the low-end content on stage minimized to reduce the most noticeable comb filtering. Rather then just clone the main mix, I'd rather build you a monitor mix minus elements that are likely to distract from stage monitoring or hurt the likelihood that the PA mix and stage spill will play nicely.
Of course, maybe he just didn't understand you. But maybe he had non-crazy reasons for wanting to dial you up a what-you-need monitor mix from scratch.