My thought is that, the reason for this rule is for privacy concerns, but then, I might be wrong, so my question is "are there or is there any security issue(s) related to using or reusing a particular or one single bitcoin wallet address for a very long period of time?
Just for privacy reasons.
But some people are still using different addresses for different transactions but in a way many of their addresses can be tracked. An example is a person that receives 5 transactions, making it 5 inputs and sped ing the whole coins with 5 inputs in a transaction, this will be easily known on blockchain explorer that the whole give addresses is belongs to the same wallet.
Another issue are that people are making use of light clients, they depends on central servers as they are not running full node. Central servers can connect many addresses generated by the same wallet together and linked it to their IP addresses.
For privacy, the best is to run full node like on Bitcoin Core or having your own Electrum server.