Are all these for their own use or any of these are for export?
Don't know what's on their mind but I can guess it's gonna give few sleepless night.
These ships are for China's navy, not export.
While these ships are being built, there are ships that need to be retired and replaced.
Example, destroyer hull No. 109 is 36 years old, DDG 110 and DDG 134 are both 34 years old, they are still in service though in training roles. DDG 164 is 31 years old, DDG 165 is 29 years old and DDG 166 is 26 years old.
These 6 ships belonged to 051 class destroyers and are obsolete.
Besides replacing these old destroyers, China would need more major war ships for escort duties for the new aircraft carrier combat groups. And with increasing need to protect Chinese interests, especially in major shipping lanes.
And the last as other posters wrote, to prevent wars and conflict. When China did not had strong navy and airforce, these was what happened :-
From 1920s to 1949, US and British war ships sailed upto 1,800 KM inside China, on the Yangtze River. During Vietnam war, US jet fighters frequently flew over South China, US war ships and its ally intruding Chinese territorial water (eg. Aussie submarine spying in China water off Shanghai in 1960s). These were done with intention to escalate tensions and could had started war.