Question

why do roses have reproductive parts when they cant even produce seeds ? and why the flower they cant produce a fruit?

Answer 1

Rose plants do produce seeds. After pollination the rose fades and petals fall off. The base of the flower swells up and develops into heps. They don't form edible fruits but these heps structures contain seeds. Seeds from these can be used to propagate rose plant. The seeds are generally not used for the propagation of rose plant as the plants which develop from seeds are different from the parent plant. So, vegetative propagation is the most common method for rose propagation.