It's been five years since the Sharks were in the playoffs. (2018-19 season) Diehards continue to attend games, but many have stopped due to quality of play/record. (And many key players have been traded away/retired. ) Those facts alone can account for low attendance.
87% renewal rate of STH for 24-25. And many expressions of interest after winning the draft lottery. Hope for future attendance improvement.
But those facts have little to do with the lease.
IIRC Hasso Plattner is the richest individual owner of the NHL. And he loves SAP Center.
Since the building opening 30 years ago, extensive renovations have been made. Including center scoreboard (on 3rd generation), ice plant (replaced, including under slab piping), escalators (replaced), seating (replaced), facia board on edge of upper rim (installed), roof system (upgraded) allowing more weight to be hung for modern touring musical groups, improve water temperature in bathroom sink (so not ice cold), and more.
With proper maintenance and upgrades, the facility will be useful for many more years.
(The Google construction in the area has more impact. And that's another story entirely. )