Most people have got better things to do with their time/life than gambling on the financial markets. If someone had started DCA'ing $10/month into SPY in 1990, they'd be sitting pretty comfortably now. Just the $1,200 they invested in the first year alone would now be worth $23k. Do the math!
If someone bought US $30 worth of bitcoin in 2010, they would be a US $ billionaire right now no DCA needed, lump sum buy and hodl
$100 a month into SPY is a WOT....10k a month into SPY is a wot....SPY is a wot. Think about it...if SPY continues on its meandering pace upwards it would double in about 3-5 years...so if you invest 100k you double it in 3 years lets say. I could 2x that just in MSTY lol.
The US stock market has a long enough history/track record, that you could be confident that starting DCA'ing monthly into SPY now would leave you comfortably off in 30 years time. In any case, what's the alternative for people with day jobs who don't want to spend their free time gambling on financial markets?