Generally speaking, addons are not always reviewed in the strictest order.
For example, some addons require admin review which take longer.
Some addons are tiny with few lines of code. They can be reviewed in minutes.
Then there are addons that are larger that some operating systems with 100,000s lines of code. Those often take a long time to review.
It is the same with upgrade reviews. Some upgrades are just 1-2 lines. On the other hand, some upgrades are massive.
There are other issues such minified/obfuscated code, using risky APIs etc that require longer to review.