I never understood why ASX companies generally only buyback...

I never understood why ASX companies generally only buyback their shares when they are making good money ..by that time it is usually the top of the cycle and the share price has usually run well...well yeah by buying back shares now the KI mine's EPS will end up be greater and us shareholders who stick around should in theory get higher divies.....
Even a 100 million share buyback intention would put upward pressure on the share price and the company could choose to only buy back on pullbacks...makes sense