The cracks on the walls appear because of variation in temperature in a particular region. If the temperature variation during day and night is more, during winter and summer season is more, then the chances of cracks on walls is more.
Poor Paint job: While painting your entire home, there can be chances of tempting to rush through it so mistakes can happen. Missing out layers, or not letting previous layers completely dry can hamper your overall efforts.
Low-quality paint: Cracks on the walls are mainly due to inferior quality paints which result in poor paint adhesion on your wall. Using different paints for each paint coat will also cause cracks on the wall.
Impatience during plasterwork: If you are not letting cement plaster completely dry before applying paint will leads to cracks.
Weather changes: Your home's structural materials expand when the temperature gets warmer, and they shrink when the temperature drops. Due to this, the cracks can be formed on your walls.