I think they must be for a foreign enduser. The M240 series MG has fully replaced all M60 variants in the army and usmc, as it is a more reliable and robust system than any M60 variant. The last time I saw the M60 in service was around 05, and they were the D variant on helos. They were replaced in country by M240 D variants, and the M60D's were going to be shipped back to the US for either destruction or mothballing, but my unit rescued a quantity of them. We used them on vehicles as back-up systems to the main turret weapons (MK47 AGL's, M2 50 cals, and M134 miniguns). Some were also placed on standard M122 tripods on guard towers. This reutilization wasn't typical, as we had more latitude than most units when it came to these things. In SOCOM, the M60E4 which was designated the MK43 soldiered on for a while in SOCOM, primarily in NAVSPECWAR units, but was replaced SOCOM-wide by the superior FN MK48 LMG starting around 2004, and was fully integrated by about 2008 in SOCOM. I don't believe the MK48 has been issued outside of SOCOM yet. Some MK43/M60A4 MGs were released from NAVSPECWAR (having been replaced by the MK48) and saw limited use by some USG contractors overseas. The last time I had my hands on one was around 2015, I never saw any in afg as a contractor but I was told that some MK43s had made the trip to iraq.
I suppose M60 variants MIGHT be in use in the conventional navy or usaf, but it seems to me that with all of the M240s and M249s available, even those services would have upgraded by now away from these legacy weapons and the support required for them, but I could be wrong. Of course, different variants of M60s will probably always be in arms rooms of SF units and the schoolhouse, but not as deployable mission weapons- they are maintained with other obsolete US and foreign weapons for training purposes, and don't even leave CONUS as "mission equipment".
Even with the improvements of the later M60 variants over the older VN era legacy M60s, the newer ones did not have the reliability of the M240 or the MK48, or the expected service life. This is due to the metalurgy in the receivers- metal fatigue would cause them to stretch "out of spec" and worsen the reliability issues. Even on the newer M60 variants, there were still components that could be accidentally installed backwards. The biggest advantage the improved M60 variants have over the M240 is lighter weight, but this is offset by reliability and controlability, especially in sustained fire. The only advantage the light M60 variants have over the MK48 is a SLOWER rate of fire- about 600 RPM VS about 700 RPM. In my opinion, about 500 RPM is the perfect rate for a general purpose 7.62 NATO machine gun.