Please refer to this UserVoice post about it: Export JPG/PNG(any format) in same folder of AI file (like before) – Adobe Illustrator Feedback
Please add your votes to the UserVoice link above.
We had changed the behavior based on user feedback that the last exported location is being reset on file open. The complaint looked valid hence we changed the behavior to ensure last exported location is always sticky.
This, however, has disturbed workflows of users who had adapted to the earlier limitation. We are looking to solve this by making export location stick with every file. Here is an illustrative example of what will happen once this is fixed.
1. Open file A – when you click on export since this is the first time export is attempted it will open the folder from which the file was opened. Now change the folder for export and export as you would normally do.
2. Open file B – when you click on export since this is the first time export is attempted it will open the folder from which the file was opened. Now change the folder for export and export as you would normally do.
3. Now if you come back to File A and export again it will show you folder chosen for File A and not File B. as we would make last export folder stick for each file.
Post your comments on this thread or please join our prerelease and engage with us. Link to join pre-release: http://adobe.ly/1Q3rCPI