Because he doesn't need that millstone at this stage in his career right now. At the moment he is relatively fantastically successful at AFC Bournemouth and nowhere else. That's not to say that he wouldn't be, but let's let him have a few years of ups and downs to harden him into a manager who can take the good and bad together. Besides, I'm selfish for AFCB.
I'm not sure Howe was ever in the frame, but I suspect he would have had the good sense to turn the job down anyway. I'm not suggesting never. Just not now.
England need a strong leader. For far too long they have had Yes men [besides Capello], and each appointment has been all about getting the players to play to their potential, rather than the usual underwhelming stuff, with the occasional proper performance which makes people believe [not me, and I suspect not you] that all is once again well. So it is not about style, but about leadership. A strong leader may be able to turn around this England Disease juggernaut, which continues to roll on to more self inflicted damage. The failure of properly capable players to play at anything like their potential continues to dumbfound, but to me it is the combination of playing favourites out of form and fitness, playing favourites out of position, playing players who cannot fit into the team, playing players without each individual really knowing exactly what his job is, and therefore no real detailed plan.
But let me get back to Howe and Allardyce. There's no doubt Eddie has huge potential and talent, and promotes excellent modern football, but will he have the respect of Rooney and Co.? And by trickle down, the others in any squad.? Howe has to show a real measure of success in the Premier League before he'll get the respect he deserves from England players, rightly or wrongly. He'd do wonders with an U21 squad, but what a waste that would be [I'm doing the AFCB thing again].
Allardyce has been there, done it, and achieved, albeit with teams of lesser players overall, and he's never had the chance with a top team. Myself, I'm not a fan of his default cautious style, but he has often also chosen styles that suit the group of players he's had available rather than imposing styles that his players can't play. Hence he's pragmatic. That's a quality I like. He's also a strong leader who does not leave anything to chance, because of his attention to detail. England have never appointed such an English manager as Allardyce, never having the balls to let a manager ruffle feathers, and when they did, with Capello, they effectively sided with the players. And they've only given Allardyce two years anyway, so he has to deliver or get out. If he can solve the equation of English players playing badly for England at important times then he will have done more service to the job than half a dozen others. And perhaps, in 5 to 6 years time, Eddie Howe can jump into a position where his talents can fully exploit a rejuvenated England setup, having proven his pedigree.