his book value is 7.6, his salary is 3.5 net, 6.3 gross.
version a: you let his contract run out, cost for 2019/20 is 13.9, and you have to buy a new dm for next season.
version b: one year extension, with the same salary and half the amortization the yearly cost is 3.8+6.3=10.1, you have a squad player for next season.
version c: 2 year extension, no raise, ~8.8 yearly cost, squad player for 2 seasons. that's very cheap at current juve level. and it's just the finances, not considering how useful can blaise be 2 years from now. also, i doubt that paratici would do anything to not to lose a 30+ year old player on a bosman. and we're not considering the opportunity cost either.
anyway, diff between b and c is 1.3m. most bean counters would certainly care, but i think the club simply rates him.