Let me try to explain in different way. If you are at exam and you are trying to score as much as possible. You see you have 5 minutes remaining with 5 questions 3 easy, 2 tough problems.

if you will start with trying to solve easy ones first then going for tough one. You will have better chances of scoring.

Or if you will try to solve tough ones first, then maybe due to time pressure you might make mistakes and have to re-do solutions midway. Scoring less because you couldn't do easy ones too because no time left for them.

Here same with bowling team, if they would send their less experienced bowlers first, they are giving batters chance to score much because this bowler might not perform well under pressure or batters can read them well.

But if you send your best bowler first batters will still try to hit him, but they would also feel the pressure and maybe make mistakes while trying to maximize runs and gets out.