Why is tertiary sector job growing?

Simple Answer...

Coz agriculture sector has 65% of population but contributes to only 15% of GDP.

but tertiary sector has 15-20% of the population but contributes to 65% of GDP.

Due to industrialization....primary and secondary sector modernized thus creating more chances of employment and greater payment of work.

Tertiary sector's industries and HQ's are all set up in cities and offer greater salary...facilities...standard of living...job security [sometimes] and insurance [not in all industries].