Maybe to not have any Bitcoin-related traffic appear in a DPI system?
Or to not have the ISP know OP is using BTC?

Without knowing where geographically his node is located (i.e. if it is not a second machine 1 hop away from his main pc), there can be multiple reasons why one would want to connect to his own node / electrum server via Tor.
Privacy is the number 1 reason here i'd say.