You need a carrot.
You probably aren't telling them what they're doing wrong, how they can improve, or what they can improve on. You're probably just beating them one after the other and that's it.
I've lost fight after fight since starting back up. It hasn't deterred me because I have given myself a carrot on a stick. A sort of constant guide of improvement. Most people don't have that. So likely, you're probably just kicking their ass and they have no idea how to improve. Fighting game waters are thick and murky. You need a bit of light to make out whether you're going to walk into a trap or if the waters grow deeper. You could easily go the wrong way. Or concentrate on the wrong things and limit your progress and potential. Going at it alone is hard. You should be helping them.
1. Explain what their characters game plan is. Don't assume they already know. It takes months for it to click and if you're making that assumption, they may never know. If you explain it, it will give them drive to work on it. Carrot. Stick.
2. Tell them what they're doing wrong. People I play USFIV with? We critique each other constantly. "You could use more hazenshu, I should be backing up from you" "Kay, let's get more aggressive next match then." "How do I beat that standing HK?!" "Try cr MK." "You're not utilizing your fb timing. I don't feel pressured by your fb's. You realize you can buffer an fb and fire one out the second it lands on block, right? Shoot them out at different speeds to keep me guessing!" If you're not being a factor in their improvement, you're doing it wrong, I feel. You should be fostering an environment where it's beneficial for both of you, so you both get incrementally better fights.
3. Tell them what they're doing right, that way they continue in the right direction.
4. If they're having trouble why not just say "fuck fighting, let's go to training so I can help you with your fundamentals" and work on those in the lab? Dude on my friend list the other day saw how I was seeking to be better with my Chun. We went straight to the lab and we had an hour long training sesh. "Try this bnb combo." "Use these buttons for situations like that." "That's a great AA. Use it!" "Walk back and forth and try to catch my moves. I'm going to teach you footsies." You said you're fighting dudes that don't know bnb combos. Why aren't you TEACHING them bnb combos? After I was taught Chun bnb I started making my own which add my own spin. Teaching matters.
If you're fostering an environment where you think they'll get better just by sheer willpower and matches, then you're failing as an experienced player. As an experienced player you should be constantly offering tips and suggestions on how to improve to help them reach their potential so you can have a larger pool. But a lot of experienced players ain't into that.
If they're having trouble with the skill gap, guide them. Show them how much they've improved. Help them work on their fundamentals. Take them training mode to work on the basics of their character. Tell them what they're should be doing more and what they should be doing less. Be more proactive in your approach to newbies.