Spielberg also only works for a huge part of the back end profits - which EON would not allow and rightly so. It´s their franchise.
I think Spielberg has thoroughly earned his share of back end profit. Usually thats because his name alone fills cinema seats, as well as it being a guarantee of a film worth seeing (even his duds qualify for that i believe).
For Spielberg not to get a good portion of the profits of a movie he's made is, perhaps as unfair as an exhibitor/art dealer claiming the greater part of the sale price of an artist's painting. It's sadly the way of things that the talented are exploited wholesale, but the likes of Spielberg have clawed back that power with their talent, hard work and a little luck.
I concede that Bond is an odd fish in this sense, as it is undoubtably Eon's baby and that is why 'name above the movie title' directors of which Spielberg is probably numero uno will never make a Bond movie. But lets face it, ticket sales on Craig's Bonds may be spectacular, but if Spielberg directed one, then no matter it's quality, or critical reception, i'm guessing it's ticket sales would dwarf all that came before.
If for no other reason (although there are many) i think that all and sundry would flock to his Bond movie out of shear curiosity to see the great Spielberg's Bond. If that were the case - that Spielberg's name had enticed many new, old and curious into the cinema, then surely it's fare that he get a share of the profits he'd created - his usual back end deal.
I'm not saying i want a Spielberg Bond movie at this point in time (although back in his prime, in the 70s/80s he'd have nailed it for sure), but i'd relish the prospect of seeing what he does with it - who wouldn't?
Tbh i imagine Eon feel the same way about the justification of Spielberg's back end profit and would not insult him by inviting him to direct without that. But that choice is an economic one, not artistic - they want all the cash themselves and that's a shame. There are many other name-above-the-title directors in their prime whom i love to see direct Bond, but won't because Eon do not like to share the profits.