Several manufacturers besides McDonnell Douglas and Lockheed pursued trijet designs, though the configurations varied considerably in how the third engine was integrated. True all-tail-mounted trijet airliners include the Hawker Siddeley Trident, which entered British European Airways service in 1964 with all three Rolls-Royce Spey engines clustered at the rear fuselage in a T-tail arrangement, and the Soviet-built Tupolev Tu-154, which used the same rear-mounted trijet layout and became one of the most widely produced airliners in the Eastern Bloc. Yakovlev also built the smaller Yak-40 and Yak-42 regional jets on the same principle, putting all three engines at the tail to keep the wing clean and minimize FOD ingestion on unimproved runways common across the Soviet domestic network. In the business jet world, Dassault has kept the configuration alive and thriving: the Falcon 900 series and its successors, the 7X and 8X, still fly with three engines mounted at the tail, giving them the range and single-pilot-friendly handling characteristics that operators value today. It's worth distinguishing these from the DC-10, L-1011, MD-11, and Boeing 727, which are trijets but not "all-tail" designs—those aircraft mount two engines conventionally on the wings and only the third engine through an S-duct or straight-through tailcone inlet at the empennage.
For working pilots, the distinction matters operationally as well as historically. All-tail trijets like the Trident and Tu-154 offered a clean wing with no engine-out asymmetric yaw from wing-mounted powerplants, simplified single-engine handling in certain failure modes, and reduced ingestion risk from unprepared or gravel strips—an important consideration for Aeroflot's vast network of remote Soviet airfields. The tradeoff was structural complexity, a heavier and more maintenance-intensive tail section, degraded aft center-of-gravity management, and the S-duct inlet's notorious sensitivity to airflow disruption at high angles of attack, a factor implicated in several 727 and Trident-family incidents involving deep stalls. These same tradeoffs are why Dassault's tail-mounted trijet business jets require careful attention to center-of-gravity loading and why type training emphasizes the aircraft's stall and pitch characteristics more than a typical underwing twinjet does.
The second half of the question—why domestic short-hop airliners aren't built this way anymore—gets at one of the defining trends in commercial aviation over the past four decades: the near-total triumph of the twinjet. Trijets, whether wing-and-tail hybrids like the DC-10 or all-tail designs like the Trident, existed largely because early high-bypass turbofans lacked the thrust and reliability to satisfy long-haul or overwater routing requirements with only two engines. The expansion of ETOPS certification through the 1980s and 1990s, combined with dramatically improved engine reliability and bypass ratios, eliminated the operational justification for a third engine on nearly every route category, including the transcontinental and short-hop domestic missions the question references. Modern regional and narrowbody aircraft—the Embraer E-Jet family, the Airbus A220, and the Boeing 737 and A320 lines—all standardized on twin underwing-mounted engines because that layout offers easier access for maintenance, better fuel efficiency per seat-mile, lower parts and overhaul costs with one fewer engine to support, and simpler engine-out procedures that today's two-engine airliners are specifically certified and crewed to handle.
The broader arc is one of consolidation around efficiency and cost rather than aerodynamic novelty. Trijets persist today almost exclusively in the ultra-long-range business jet segment, where Dassault's tail-mounted layout supports the extra fuel reserves and redundancy premium buyers want for oceanic and polar routes, and where cabin and baggage volume benefit from keeping the wing box uncluttered. For airline pilots, the disappearance of trijets from domestic fleets reflects decades of engineering and regulatory progress that made the twin the default answer to nearly every mission profile once reserved for three- or four-engine aircraft. Business jet pilots transitioning into or out of Falcon types are really the last cohort flying this once-common configuration, making familiarity with its center-of-gravity and single-engine-out handling quirks a niche but still relevant skill in the modern training pipeline.