Per 14 CFR 399.85(c):
Agents may provide this information in text form in the e-ticket confirmations or through a hyperlink to the specific location on airline websites or their own website where this information is displayed.
In my reservation confirmation emails:
Carry-on baggage: On Alaska Airlines flights, each traveler is limited to one carry-on bag plus one personal item. See our
carry‑on baggage page for the latest policies and size information.
Checked baggage: Alaska Airlines rules and fees apply for this itinerary. See the
checked baggage page for details and exceptions.
Also, it's easier for AS to change baggage fees on their website and when linked, the customer will always get the most up-to-date fee structure. A fee hard coded in an email will not dynamically update if AS decides to change baggage fees, potentially leading to even more confusion down the line.