You mentioned the inability of the WRs to get open (ie separation). Others have also brought up the WRs as a reason the numbers are starkly different from last year. But the WRs aren't materially different from last year, so it's not clear how this would now be a significant factor as to why Josh's sack and pressure numbers are up, despite him having career highs in accuracy (bad throw %, on target% and drop%).
I agree sacks are the result of several variables, but the difference in this year's WR performance and last year's doesn't seem to be a significant one.