Um, no.. it's not because he's lazy. It's because he doesn't know what you want him to do. If he hasn't been trained to jump or even started by someone who knows what they are doing he has no clue what you are asking him to do. He may have jumped a fence before, but that was without you on him. There is a HUGE difference... You can't expect to just get on your horse and him fly right over a rigged up 2ft jump. That's like expecting a horse to gallop the barrel pattern just because they can gallop and turn.. There is a LOT more work and training you have to put into it before you can expect him to understand what you want him to do... Just because he can jump does NOT mean that he knows how to jump correctly, especially with you in the saddle.
Say your teacher gave you a math pop quiz..You hadn't seen the material before hand..but you can count, add, subtract, and such.. How would you do on an algebra test that you had never seen the material for? But your teacher expects you to be good at it right then, without practice or prior knowledge about the problems in the quiz.. You would fail at it.. It's the same concept with your horse.
And whacking him with a crop to get him to jump the jump will only create problems in the long run..If you want to jump, be responsible and get a trainer or someone to help you and your horse.
I am Sparkly Meanie Doodie Head and I approve this message!