How are a sinkhole made and why are we hearing of so many lately big enought to eat a car or even a house?

Answer 1

There is one near my house and it's huge. Of all places, it's at the main entrance to a beautiful subdivision. Once they start breaking water lines or sewer lines, they become a nightmare for nearby residents. And that's exactly what's happening for these poor folks. I did find this on the web:
Sinkholes are all about water.
Water dissolved minerals in the rock, leaving residue and open spaces within the rock. (This is called “weathering”.)
Water washes away the soil and residue from the voids in the rock.
Lowering of groundwater levels can cause a loss of support for the soft material in the rock spaces that can lead to collapse.
Changing groundwater gradients (due to removing or introducing water to the system) can cause loose material to flush out quicker from the voids and the surface to collapse in response.
Any change to the hydrologic system (putting more water in or taking it out) causes the system to become at least temporarily unstable and can lead to sinkholes.
Sinkholes can result from seasonal changes in the groundwater table, freeze and thaw of the ground, and extremes in precipitation (drought vs heavy rain).
Karst landscapes develop naturally through the weathering process so a sinkhole can be considered a natural occurence. But, human influence causes sinkholes to occur where they might not naturally have happened. Or, they may occur sooner or more abruptly than under natural conditions.

Typical activities that can lead to sinkholes are:
Decline of water levels – drought, groundwater pumping (wells, quarries, mines)
Disturbance of the soil - digging through soil layers, soil removal, drilling
Point-source of water – leaking water/sewer pipes, injection of water
Concentration of water flow – stormwater drains, swales, etc.
Water impoundments – basins, ponds, dams
Heavy loads on the surface – structures, equipment
Vibration – traffic, blasting
Sometimes several factors combine to cause a sinkhole. A sinkhole left open to take more water may continue to grow and can contribute to the appearance of more sinkholes nearby.

Answer 2

When water is taken from the earth and the earth cant make the water that fast the surface caves in and the size depends on the water taken.

Answer 3

It's getting common in the southwest US where we take water out faster than the groundwater can replenish.