Oracle tools are not optimized for developers of today. A key selling point to enterprises is your developers could be more productive with their point and click IDE/interfaces.
These days with the tooling around open source I believe you can get things done much faster (and have done this) the code is more maintainable etc.
Second disadvantage consider oracles commerce framework atg. They have their own concepts and terms for things that are in open source solutions making it confusing for developers familiar with open source frameworks. This could be on purpose to sell more consulting for partners.
Next the is the cost of training and up skilling junior devs. With open source you could probably teach yourself try searching for oracle atg tutorials. Check the # of stackover flow questions vs magneto.
Fourth: I have seen people who are "oracle developers" (fusion, odi, erp, atg etc) are mostly just product specialists. Give them a text editor and tell them to write something and deploy to a paas , commit to version control and they struggle.
Finally the software tends to be ops heavy encouraging bad practices like no version control or automation.
All of these factors are not considered in the purchase or "ROI" calculation, but some of them could seriously hurt your return.
I have seen companies spend millions in implementation of an oracle product only to use < 10 % of features and the same business objectives could have been achieved at the fraction of the cost.
* excuse typos on mobile