Not everyone is the same, my wingspan is half a foot more than my height, it is very hard for me to add mass to my arms. I've been lifting heavy for almost 2 years now, compound lifts and pull-ups with some slight isolation work has had very little effect on the size of my biceps. I've worked out most body parts twice a week with the exception being my biceps because I listened to people say they will get hit in other ways, and that hasn't worked for me.
I'll have results in 2-3 months and I'll post them.
Your arms will get hit "adequately" from compound lifts such as the ones you mentioned but if you're trying to get big arms, you need to do direct arm work. No question there.
The issue that I assume people have with what your bicep work is now is that it seems there is no plan. Doing 50 reps of 6 pound concentration curls .. or sets of 10 with a 25 pound weight for as many sets as possible until you fail and can't do another set -- that's not a plan. That's a recipe for stagnation. Nobody does that, and nobody would recommend that.
I don't know what your gym equipment situation is but I am assuming you work out at home since you said you curl during NBA games. If so, you CAN progress perfectly with limited number of weights.
1. Keep things simple.
If I did read you correctly, doing 50 reps with 6 pounds for concentration curls is basically jacking off -- so you could drop that. If it's 50 pounds for 6 reps, correct me ..
Pick 1-2 exercises and run from there. For biceps, standard dumbbell curls should be all you'd need for direct arm work.
2. Plan out a progression map for curls.
I am going to assume again you only have a 25 pound dumbbell. Here's an example of a solution to how you can progress for many months without adding a single pound to your curls:
Week 1 = 3 sets of 8 reps @ 25 pounds
Week 2 = 3 sets of 10 reps
Week 3 = 3 sets of 12 reps
Week 4 = 3 sets of 15 reps
Week 5 = 4 sets of 8 reps
Week 6 = 4 sets of 10 reps
Week 7 = 4 sets of 12 reps
Week 8 = 4 sets of 15 reps
Even at the same weight, you WILL be stronger and provided you are eating enough to fuel growth, your arms will likely get bigger at the end of 8 weeks. The issue is if 25 pounds is enough for your starting point. If you can curl 25 pounds 30 times then this program wouldn't be that effective. If you can curl 25 pounds 12 times then this would be much better.
Ideally, you would add 10 pounds at the end of the 8 weeks and then start again.
Progression is progression. As long as you have a plan for progression, you're fine.