In addition to the bad coaching (worst of Pop's career) and player declines/underperforms of Aldridge, DeRozan, Poeltl, Rudy ...
Front office mistakes are coming home to roost.
The team has had only 2 concrete avenues to improve the roster: the MID-LEVEL exception and the draft.
They've blown the MLE two summers in a row. They initially were using it to get Carroll, who just isn't playing. And Marco last year was a terrible signing and he shouldn't ever play. Lyles doesn't happen without Bertans getting traded, so not what I would consider a straight MLE deal. Just because he starts like bogans doesn't mean like Lyles is doing great either.
Then they draft the opposite of their signings. They sign 'win now lol' guys in their 30s like Marco and Carroll, but draft developmental guys. They could have drafted an NBA ready shooter like Huerter over Lonnie, and Huerter was better than Marco before he ever played an NBA game. They could have drafted Thybulle or Clarke over Samanic. Clarke just shot 2-2 on threes on his way to 14 & 8 in 18 minutes against the Spurs. Maybe he's not 'ready' to perform in the deep playoffs, but he's more than ready to beat on mediocre and bad teams like San Antonio.
Spurs were trying to have it both ways and are losing big. Can't 'win-now' when the washed up guys you sign play like washed up tragedies or not at all ... But also don't want to replace them with young draft picks because the young guys 'aren't ready' or need years of development or maturity or whatever.
If the team had decided on 'compete now because Pop deserves it, no rebuild for Pop!' as it seems they did with DeRozan and the signings etc, then they also needed to draft NBA ready players to blend in with goal.