Greece is hotter than drier than normal. But the big problem is that it's also windier than normal.
Arson is a problem every year, but because things this year are hotter, drier and windier, the arson impact is worse. It's a bit like Australia:
https://en.wikipedia.org/wiki/Bushfires_in_Australia
The most destructive fires are usually preceded by extreme high temperatures, low relative humidity and strong winds, which combine to create ideal conditions for the rapid spread of fire. Severe fire storms are often named according to the day on which they peaked, including the five most deadly blazes: Black Saturday 2009 in Victoria (173 people killed, 2,000 homes lost); Ash Wednesday 1983 in Victoria and South Australia (75 dead, nearly 1,900 homes); Black Friday 1939 in Victoria (71 dead, 650 houses destroyed), Black Tuesday 1967 in Tasmania (62 people and almost 1,300 homes); and the Gippsland fires and Black Sunday of 1926 in Victoria (60 people killed over a two-month period).