The answer blames socialist programs for Venezuela's current problems. Many north European countries have these programs and more and yet are rich. There must be another difference.
Yes, there's the resource curse, also known as the Dutch Disease - but Norway has made a huge success for Norwegians on oil (OK, about the only country that has) and the key difference is that oil profits (a tax rate of nearly 90% on the oil - 10% still made Shell very rich) is being held in a sovereign trust by a non-corrupt government. Institutions.
This video from The Story of Life on why, out of nearly 200 countries, about 25 are rich and the rest are poor and most will probably remain that way.
https://www.youtube.com/watch?v=9-4V3HR696k . But it's not a new thesis. I think most theories would agree, the 2 most important factors dwarfing all others are institutions and corruption (and I reckon they're almost the same, have good institutions and there'll be little corruption, have high corruption and the institutions will be corroded).
Unlike Norway, Venezuela has high corruption that haemorrhages wealth into overseas accounts and fragile institutions that at best is incapable of confronting that corruption.
Transparency International ranks Venezuela in the top 20 most corrupt nations, ranking equal 8th with 3 other countries. https://en.wikipedia.org/wiki/Corruption_in_Venezuela
Chavez was elected in Dec98 on the platform to write the constitution to address corruption. It wasn't, and that's why it's poor and will remain that way until that is addressed.
Answer is: corruption, corrupt bureaucracies, corrupt businesses & corrupt institutions.
(I'd like to think well of people, and thus I think Chavez may have had good intentions, but 2002 coup rattled him. His army was corrupt and he had to adapt and became as corrupt as his army to regain it - impressive from a Machiavellian point of view - sad for Venezuela)