Because abraham doesnt believe tassy is different, and tassy is too scared to leave. thats one of the objects of the storie, jeremiah has to convince tassy to step up, while convincing abraham to trust her ( its all in a matter of once jeremiah gets abraham to trust her, he will do it on his own. anything else?
oh i guess i didnt tell ppl how he does that.....welll.....
theres a outside section, and he climbs over the fence. well, theres a window in Tassy's room,( which is beside the outside world) and he simply pops open the window to get in. ( how he pops open the window just use ur imagination..;)