Because the faucet is easy — it's the 40-year-old shutoff valve under the sink that snaps mid-job and floods the cabinet. We've seen it a hundred times.
A licensed plumber handles whatever the job reveals — corroded valves, worn supply lines, a drain that needed resealing anyway. Done once, done right, no callback.
And that drip you're ignoring? It's real money: one drip per second wastes about 3,000 gallons a year.