It's not that straightforward; there was concrete on top of the soil, it had functioned as designed for many years. There are problems with infrastructure main

It's not that straightforward; there was concrete on top of the soil, it had functioned as designed for many years. There are problems with infrastructure maintenance at a national level, and lots of deferred maintenance/upgrades. Given that, there's no reason to suspect that upgrading the spillway prior to failure would have seemed like a higher priority than many other remediation projects. There was not an a priori way of knowing it was going to fail, instead of a bridge abutment or whatever else was presumably repaired first, and would have had to wait if the spillway work had happened first instead.