It's a very sad loss and we can only pray right now for the safety of those whose homes were damaged.
Not meaning to be unsensitive, but from living in Japan (Where mudslides are not uncommon in combination with earhquakes and heavy typhoon rains) looking at Google Images and doing a bit of reading I think I can see the reason for these mudslides.
These are areas where in the past there has likely been heavy de-forestation (& some replanting of conifers - which don't have very strong, nor deep roots). Many gardens in pictures show large areas of grass - which really doesn't help soak water deep into the ground & distribute it when there are heavy rains... The roots of grass are only as deep as the grass itself and it's also not strong and then it acts as a ground cover, where nothing else of significance grows.
And so the water sits not far below the surface with nowhere to go...
Hardwood trees tend to have the deepest & most widespread roots and would be what should have been re-planted & maintained in areas where there is danger of landslides. The height of a tree is roughly the depth of the main root. Sadly, people placed a lot of value on large hardwoods and so these were cut down a long time ago and the trees that replaced are just pioneer species which grow very quickly and are much easier to culture but don't offer much safety through deep & strong root growth. Being evergreens, the land doesn't get much exposure to sun (especially in winter where deciduous trees lose their leaves) and so it's got a lot of water stored in it and the soil around such trees is usually soft.
With heavy rains, as there are no deep roots to channel the water down deeply, the land gets soft & heavy with water and then as there's no underground structure to bind it together - it can eventually slide. Mining of the sides of mountains to make roads, infrastructure, etc. can also weaken the hillside structure.
It's amazing the lack of basic understanding that local governments have into what re-generates water and how to make it work to our benefit. In the UK they've had severe flooding this winter and people think it's just an act of nature, but they fail to realise that forests have dissapeared to be replaced by farms with grazing for cattle (Farmers are actually susidised by the government for creating larger areas for animal grazing!).
To see the effects of de-forestation you only need to see the colour of the water in rivers during & after heavy rains and witness how much soil is washed into the rivers. Then look at old growth (hardwood) forests and the lack of silt in the rivers around and compare the difference. More hardwoods are what should have been grown to prevent disasters becoming a consequence of de-forestation in previous decades.
Euro RC51 SP2: HRC WSB Ti Hi-Level, T1 Airbox & Snorkel, PCIII, Dymag CA5 Carbon Wheels, Ti64 Spindles (F, R & Swing Arm), Mori Link, Maxton GP7 Shock & Ohlins 832 Forks, Brembo GP Calipers & SBK narrow track (F), Braketech Disc (R), Brembo billet Underslung x 2 Brembo RCS, Tyga Triple, 7075 Stem, Probolt Titanium all over, Babyface rearsets, MR Complete Carbon Lineup, Custom Undertail & CBR 1000 LED, Watsen LED Indicators, Harris Brace, Giles clip-ons, Corbin seat, etc. 2013 BOTY.