Surprisingly Jimmy playing back to back tests, makes sense because for them series is on the line and they'd like to see 2-2 after 4th test match.
Why would that be a surprise for Anderson to play another match?
Well, Grandpa is about to turn 42 soon. Already featured in 2 back to back test matches and playing 3rd on the trot. He bowled 73 overs in the last 2 test matches and 38 overs came in the last test.
In contrast, Bumrah is 30 yo and bowled almost 81 overs in the last 3 tests and taking a break.
Fair enough, he's shy of 4 wickets from coveted 700 wickets milestone, that might be the reason he's going to continue in 4th test.
Also, I'm seeing rain might spoil the match tomorrow.