I guess the old Merks are being reroled.
No guessing needed. The IDF produces ~30 tanks per year. Exactly enough for a battalion plus spares and experimentation.
Ever since it filled up all armored units with the required tanks and set the needed amount of brigades, it has been decommissioning tanks at a rate of 30 tanks per year as well.
Every year, one active forces' battalion gets new tanks and transfers its old tanks to a reserve battalion, whose former tanks are put out of service or repurposed.
At this rate the IDF also manages to fully replace the oldest tanks when they're only a few years short of 40. That's the amount of time any MBT is expected to serve, with upgrades, after it's produced, and it gives some time to account for possible delays that would last several years.