The original "Lifeline" program (from 1984) was intended to address a concern completely unrelated to cell phones. Remember, virtually no one even had one at that time.
A few decades ago, a very high percentage of poor households had no telephone service at all. Adjusted for inflation, it was very expensive at the time. Policymakers were concerned, not without justification, that a large number of lower-income Americans had little ability to call for timely help in case of a heart attack, stroke, or other health emergency.
That's not likely to be the case today.