Question

why ohms law is not applicable for temperature changes

Answer 1

Most of the time it doesn't apply. It applies pretty well to copper wire at room temperature, to most metals, and of course to resistors - components carefully engineered from carbon or metal film or wire to be ohmic when operated within their power limits.
It doesn't apply to electronic devices containing semiconductors, like LED lamps. It doesn't apply to gas discharge tubes - there is no current till a certain voltage, then suddenly one flows. It doesn't apply to incandescent lamps, since the resistance changes when they heat up and two in series will draw much less current than Ohm's Las would suggest. But it's such a simple law, and so useful, that it's used in in a large number of situations. Most of the time, with good reason 

Answer 2

bcz temperature changes cause change in conductivity
hence the resistance of conduct also increases
that the simple way to express