the php maintainers themselves stopped supporting php5 --> if there ever is a major security hole in the framework, it won't be fixed in reasonable time, if at all.
this means the hosters are in danger to run non-secure software on their servers, and if some 0-day exploit pops up, all they could do is let it destroy customers data until notized, and then pull the plug very fast, with no one able to export their data, etc. from that moment on (remember most people hosting things are really professionals). this is no professional policy for a service provider.
so pushing the customers out of php5 was the way to go the last two years, with lots of information about the hows and whys coming via newsletters, letters, serverlog warnings, ... at some point, shutting it down is the way to go to minimize risk and optimize costs for maintaining it in parallel to 7, 7.1, 7.2, 8, ...
(it's interesting to see that expensive, service driven hosters still support it, but you payed for it indirectly).