But, that's Mauna Loa in a nutshell. The lava coming up is relatively gas-free so doesn't do the explosive expansion when it gets to the surface. ("Diet Coke and Mentos" is a surprisingly accurate metaphor/description for why volcanos explosively erupt).

Most previous Mauna Loa eruptions have just been flowing lava without a huge amount of ash release (comparitively), so the damage done by the eruption is much more localised than e.g. Mt St Helens for similar amounts of emitted lava.