Oh, and if they wanted to invest $300/pay period into the S&P 500, note that SPY is currently at 440. https://www.ssga.com/us/en/intermediary/etfs/funds/spdr-sp-5... so absent fractional shares, you cant...
And if you invest monthly, what do you do, buy 1 share (different amount per month)? Or do you just give up and go to Vanguard/Fidelity/etc? This is sort of my point, how is something as basic as repeat-invest not available on the world's biggest bank?
Do you mean automatic deposits and investments? That's table stakes. They offer it. They aren't advertising it because fire-and-forget is 99% of the pitch of the wealth management industry. (That they're messaging it badly is in no way challenged.)
With respect to smaller dollar amounts, the traditional answer was mutual funds. Those usually have $1 minimums. They were historically shit when it came to fees, but now typically come in below 50 bps for broad-market funds.
Most long-term, low-involvement investors wouldn't. They'd buy an ETF. The exertion of selection effect for Amazon versus the rest of the market is a high-involvement action.