Well, let me correct you by going into some details. There are two ADS-B systems: the classical one with transponders extending their squawk on 1090 MHz, and the UAT system, which works on 978 MHz. The latter allows ADS-B IN (weather, traffic, data messages) and OUT (position report). However, UAT is only suitable for General Aviation and aircraft flying below FL180 (regulation starting 2020 in the US).
Typically, all new airliner and commercial aircraft since 2006 are equipped with a mode S transponder, including an extended squitter. That means that today 60 percent of all carriers are in fact transmitting ADS-B, but there are just a few ground stations (and so far no space based systems), that can read the signals. These airliners do not need ADS-B in, because they get all the data by other systems, such as TCAS (traffic) or ACARS (company communication, weather etc.). Therefore, ADS-B OUT on 1090 ES is sufficient.
Finally, I disagree with your statement that the US is only funding ADS-B OUT. In fact, the US is the ONLY country in the world that installs nationwide (nearly completed) a ground based dual ADS-B (1090 ES / UAT) system. That means that all aircraft equipped with a UAT (including my little Cessna) are receiving ADS-B IN free of charge.