The reason is that there is more "junk" out there that entails more risk to get higher yield. Better high yield bonds are getting scare. Some funds buy the riskier bonds but a good manager stays clear.
Note that Jan. distribution lower than in past 12 months, now Feb. even lower. If this new dividend payment is typical, the annual yield will be down closer to 6.2% or so, far lower than his 8% last year. Hopefully, this is short term.