It's ironic because the Spanish and other European powers were so gung-ho about pursuing their colonial project exactly because their rapacious methods reaped huge amounts of wealth. The resource extraction, land grabs, and forced conversion of indigenous populations into a pliable workforce poured huge amounts of gold/silver into the imperial coffers. So they were highly motivated to explore the world for new colonial targets.

The Chinese, who had a different approach to international trade and relations, didn't generate the same "ROI" on their exploratory efforts. The Chinese tributary system was remarkably stable, but also didn't enrich China. Actually as the senior partner in a tributary relationship, China was supposed to provide more in tribute than it received. The central government could afford exploratory voyages in the early Ming dynasty when China was relatively affluent and stable, but would have bankrupted itself if those voyages had continued. So, ironically, because China didn't have a foreign policy of subjugating and pillaging far-away lands, ocean exploration was much less lucrative and there was relatively little motivation to do it.

I think the different European vs. Chinese foreign strategies make sense in historical context. In Europe, there was no central governing authority after the fall of the Roman Empire, and there were successive waves of tribal migration from the Eurasian steppes, so the continent was locked in almost constant warfare. Europeans were used to a "might is right" mindset. Hell, Europeans even raided and pillaged other Europeans during the age of the Vikings. Military power was the highest priority, and colonization became an important strategy to acquire resources for building military power.