Traffic in, black box out
Your agency runs the campaigns and the traffic shows up. Then it disappears into the store. Some of those visitors could buy today. Most can't. The agency can't see which, the store treats them all the same, and when it's time to judge the spend, everyone argues over attribution because nobody can trace a dollar to a deal.
Campaign attribution
The agency also hits a wall it cannot get past alone. Turning clicks into ongoing one-to-one text and email means running a compliant TCPA opt-in funnel, capturing consent and managing opt-outs in real time. Most agencies aren't built for that, so the traffic stalls at the form.
So good campaigns get cut and weak campaigns get renewed, and the visitors who could have converted never start a conversation.