You're conflating two ideas.
100% stocks as an asset allocation is definitely not conservative.
However, if we look at historical data stocks long term average is ~10%. Deduct 3% for inflation we have 7%. So figuring 4% when history has been 7% is a pretty conservative assumption. It's assuming stocks perform only 54% of their historical return. Or actually 70% depending how you look at it.
That misses the point of SORR, you can have sickeningly long stretches where you can forget about gains, your portfolio is down hard but you still have to eat.
For folks where a poor SORR and/or a long life would run them out of money, the safer thing to do is wait. If you have plenty of money, then it's not a very important decision, though for married folks, the dice are loaded in favor of the high earner waiting.