The secret is surface area.
If you will notice, kindling is small pieces of fuel with lots of surface area. Lots of flame, but it doesn't last long. The main fuel, (logs) has the burning distributed over a large surface area, by volume, and, as such, gives off more heat, (burns), over a longer period.
If you're a pyromaniac, it's simple.
BINGO.
With wood kindling or paper (or liquid accelerants), smaller cross section fuel sources are easier to bring up to gas phase and ignition temperature. Second is the quantity of O2 saturation in the immediate vacinity prior to initial ignition, which once the smaller cross section fuels are consumed are only replaced as consumed.
Try to light a regular sized log, it will not flare unless you are using a torch to ignite.