Qixi (Valentine's Day in China) is a traditional festival in China. It is said that magpies come to take the overpass every year on Qixi night to bring cowherd and weaver girl (crow) together. Therefore, Valentine's Day in China is considered as the favorite festival of magpies. However, magpies are rarely seen in reality for two main reasons:

First of all, the number of magpies has been greatly reduced. Due to the deterioration of the environment, the habitat of magpies has been destroyed, resulting in a decrease in the number. So it's hard to see magpies in cities or densely populated places now.

Secondly, magpies like a quiet environment. Magpies are birds that like to live in quiet forests or rural areas. The hustle and bustle of the city often makes them feel uneasy, so they don't want to appear in busy cities too much.

To sum up, magpies are not common on Tanabata on this day, because the number of magpies decreases and they like a quiet environment. However, the romance and yearning of Tanabata are still people's traditional customs and cultural sustenance.