Then you don't know why they are billionaires. These guys are businessmen and they know that throwing away money isn't wise.
As for the prospect haul, who cares.
By 2020, Bogaerts will be on a $25+ mil per year deal. Betts is probably getting at least that much in his final year of arb. Bradley is looking like a $20 mil a year player at least by 2020. Benintendi will be in arb. Pedroia will be on the books at $14 mil. Price will still be getting $31 mil. To keep this team together, you'll have to allocate $130 mil of the $210 mil projected lux tax to 6 players with 2 of them near the end of their careers. $90 mil for 19 players, especially when two will probably be either replacement level or lower isn't feasible in this market