From an official source:

IOI 2025 was unfortunately canceled due to the inability to host it in Bolivia as initially planned. Unfortunately, Bolivia was unable to secure a suitable venue for the event, and the IOI committee was unable to find an alternative location in time. This left the committee with no choice but to cancel the competition entirely. The IOI committee expressed their disappointment at this outcome and assured the international community that they would work hard to ensure that IOI 2026 would be a successful event.