Datang: What's wrong with my fief being a billion points larger?

After traveling through time and becoming Li Yuanji, he arrived at the seventh year of Wude. Li Yuanji said that he was very panicked, as there were still nearly two years before the Xuanwu Gate Incident. Thinking about his eldest brother who always made promises to him and asked him to cause trouble, and his second brother who wanted to kill him, Li Yuanji said that he could not stay in Chang'an any longer.
At this moment, the system was activated. As long as you develop the place and advance technology, you can get rewards. The ultimate prize is eternal life. At this moment, Li Yuanji instantly had an idea.
He then requested to go to Lingnan, to take Lingnan as his fiefdom and to develop Lingnan. After that, as they watched the fiefdom growing bigger and better, everyone fell into deep thought.
"How come the King of Qi's fiefdom is larger than that of the Tang Dynasty?"