Exactly. They're front-running expected rate cuts which mostly affect short term treasuries, and like other HYSA products, you would generally expect them to lead on cutting rates as short term treasury yield to maturity declines and lag on raising their yields when short term rates are increasing (see also, gas stations setting fuel prices as a function of expected oil prices).
If you have a brokerage account, like you said, it's very easy to cut out the middleman and buy your own treasuries. You also get a consistently better rate, exemption from state income taxes, and less duration risk (i.e. you buy them at a rate with some duration, which you will get if held to maturity). You can sell before maturity if you need liquidity, and you'll likely have available funds at least as soon as you would from a HYSA ACH transfer (and maybe sooner with brokerage/checking at the same bank).
Also, treasuries are great when you have a large expense that you've saved for but isn't here yet (e.g., tuition, property tax, insurance premiums). Buy a maturity a few days before the due date, earn interest, and pay for the planned expense when it's due.
