The Tigers had 41 pitchers who ended the year on either the Detroit or Toledo roster. 9 were on the IL at season's end. 20 have hit free agency, either through traditional means, minor league free agency, or non-tender/off-season crunch. One more was traded because of roster crunch and one more was lost to the Rule 5. 9 of those pitchers who hit free agency have been re-signed.
They need depth and they straight up need to fill the rosters. They also have a packed 40 man roster, so taking fliers on major league deals forces you to put a valuable piece through waivers, so the bar there is going to be super high. Do you think they DFA'ed Malloy for fun?
Going one level lower, of the 20 pitchers (including 4 injured, one on development lost) on Erie's season end roster, 8 of them hit free agency. Pena has re-signed and was among the signings that people are blindly bashing. Kuhn re-signed as well but was nabbed in the Minor League Rule 5.
So you need roughly 55 or so pitchers in the top 3 levels, and you also want about 10-15 extra in spring training just to see what sticks. The Tigers if they sat idle, would have had 31 plus whoever in West Michigan was ready for AA minus anybody still out with injury. No wonder they are hitting the minor league free agent pitching market hard. No wonder they non-tendered Mattison, Little, and Darnell so they could re-sign them to sweetened deals and bypass waivers. No wonder they took four pitchers in the Minor League Rule 5 draft. They need the bodies.