Reason #1 the Mariners will make the Playoffs: Veteran Leadership
After seeing Teoscar Hernandez and Eugenio Suarez, not to mention Paul Sewald, all leave the team last season, the Mariners need an influx of leadership. They had JP Crawford still, but the team was missing that older player who has been there before or has the ability to lead a clubhouse.
Enter the Mitches. Mitch Haniger is back with the Mariners, and he instantly takes the mantle of team leader back. He was such an instrumental part of this team in 2022 that getting his leadership and clubhouse persona back on the team should play a huge part in how this team performs in 2024. Even if he ends up injured again, I think the role he can take in the clubhouse will positively impact the team without him being on the field.
It's not just Haniger, though. Mitch Garver is going to play a big part here as well. You're taking about an impactful player who just left a division rival that won the World Series. He's a vet with postseason experience, and it should help the rest of the team know what to expect if and when they make the playoffs again. Oh... he can rake too, which helps.
Lastly, it's the newest addition in Jorge Polanco. He's a 10-year veteran who has been in the playoffs in four different seasons. While his team hasn't always seen success, just having that presence on the team will help to calm the young or inexperienced players.