Sometimes that could be the operational use case depending upon what is required. In many cases it is possible that the turret ones are either less prone to environmental damage due to where they are or they are a bit more of a headache to take off and put on.
ERAs have weight too -
It’s more likely that the turret ERA is not removed because it’s not inherently harmful to the crew and other infantry around the tank. Meanwhile the ones on the Hull are often stepped on or could be damaged in an accident. Though ERA is very inert and doesn’t go off even to small arms fire, it’s better not to take a risk and keep it on, it is an explosive after all.
Secondly, ERA has limited shelf life, and using it reduces said shelf life, that’s apart from the added weight and complexity of keeping it on when not in a conflict.
Thirdly, another reason we often see ERA on AKs turret but not on the hull is because sometimes the plates on the turret aren’t ERA at all, they are also often extra composite plates that look like ERA, you can see the difference in some close up images.
Lastly, the way ERA is mounted on older Al-Khalid (and by extension Type 85) is different than how it’s mounted on AK-1 and VT4. On the older models, there is a large metal plate to which ERA is mounted and then that plate is mounted to the hull, you can take off the entire plate of ERA as required rather quickly.
In the newer models however, ERA is directly mounted to the Hull using mounting points, these can be seen (or not seen) in images of AK-1 and AK without ERA.
All that being said, yes, if a conflict was to start, ERA would be quick to go on, including ERA on the sides, PA does indeed use Side ERA on AK, AZ and VT4, it’s not hard to do and is not needed during peacetime, but like the field modifications we saw in WoT, this would be one of the first thing to go on tanks (if needed) during a conflict.