as a Shenzhen guy,

I'd like to say the most important reason may be the price of the land has been increased quite a lot in the last years.

Many manufacturing companies, even Huawei moved out of Shenzhen this year, some go to Dongguan, Huizhou, which are other cities of Guandong, and some go to Vietnam, Thailand.

The reason is quite simple, they cannot afford the price of land to build the factory, and the salary cost is higher since the housing rent price also goes higher. Some factory owners work hard for a year, while the incoming is even less than the value increased of lands he owns.

So the business all goes to the lands, housing, malls. People don't know where is the top, but people believe is far more yet. Because Hong Kong, the city next to Shenzhen, has a higher land price.

For the future, the great bay area may solve this issue. Shenzhen will focus on the development of high-tech technology as a research center and enterprise center. The manufactory will move to Dongguan, Huizhou. While HongKong serves as a business/finance center. Guangdong will be the transaction center.

It is possible with the highly developed traffic net. The high-speed railway connected every city of the great bay area. People and things can move fast. Taking trains has become easier and more convenient than taking buses now.