A lot of companies that offer home internet will provide a phone+internet package cheaper than internet alone. Why do they do this? Do the telemarketers subsidize it? You would think a company would want to charge extra for additional service.
I’m pretty confident the idea is to entice you away from conventional AT&T service or whatever (or entice you to something resembling landline service, if you are a cordcutter), and then once the two year commitment (or whatever period of time is stipulated) runs out, the hope is that most people will be too complacent to find an alternate phone provider when the price of the phone service goes up.
Are you sure that the quoted bundle price is the final price, and not a promotion that runs out after 6 or 12 months?
They hope to get you to make phone calls they can charge you for.
Internet-only plans are either legacy (and they are milking you for all they can get), or special-purpose (and they charge more because they know you have a special need)