Why does stuck engine lifter tick sound louder when engine is warm?

dirty oil doesnt necessarily cause a bad lifter. It will cause a lifter tap if the oil goes unchanged to long which causes the lubricants in the oil to break down. But lifters can go bad from years of use, driving the engine to hard/abusing it or a worn pushrod can cause a lifter malfunction. Lifters can stick, or even literally explode.. try changing oil first but if that dont work.. you wont know what happened til you tear the valve covers off..Good luck