Insecure people hope for support, encouragement, and validation, just as anyone else does. The difference is that they need it more, because they have difficulty giving it to themselves.
Rather than get annoyed at them, understand that they may need it more, and be willing and happy to give them that boost of encouragement. With time, they may overcome some of their insecurity, and you will have played a small role in making their life better.
If you want to avoid giving them positive energy, which they take and do not give back to you, you can choose to avoid them, don’t validate or invalidate them further, and go on with your own life. You decide if you want to take responsibility enough to care for them, when they don’t give back to you.
It’s as if they are standing on quicksand. Lend a hand, pull them out sometimes. If you can’t do it without offending them, you’re not helping them. Maybe in that situation, if you aren’t obligated, just walk away.