Why is it increment/decrement under the cursor instead of next?

[txtyash]

ctrl-a and ctrl-x don't act on objects not under the cursor whereas in vim they act on any next object.

Why is it not the vim way?

[archseer]

Read the discussion on the implementation PR

[txtyash]

So is it going to be implemented or going to function the same way?

[pickfire]

Jumping to the first number if the cursor isn't already on a number

Most of the time when I use ctrl-a/x in vim I rely on it jumping to the nearest number, so personally I do like this feature.

Based on what @archseer shared, he shared the link to current implementation done by @sudormrfbin which explains why it behaves that way. It's not a bug, it's a feature.