Lecaviler makes an average of 7.2 Million over the remaining lifetime of his contract. You buy him out you're effectively paying 4.77 per annum and getting nothing in return, saving ~2.4 million a year in player salary. A replacement top nine forward, less good that Lecavalier, is easily going to eat up that 2.4 million, leaving you with no real cash savings.
Unless you think Lecavalier is going to be worth less than a 2.4 million dollar player on average for the remainder of his career, buying him out doesn't really make sense.
Now if a wealthy team like MTL, PHI, NYR etc. held that deal, a buyout makes perfect sense because you care more about cap hit than dollars. But TB operates under different constraints.
For a team more worried about cash than cap, it makes no economic sense to compliance buyout Vinny.
It would be a smart move with compliance buyouts there were last time were you payed 1/3rd of a years salary and were done with them, but the current regime does not favor dumping him.