Same reason you don't see dimelines anywhere else, greed (or the need to maintain a profit).

Yes, hockey ml's are similar to bases, but unlike bases there aren't 15 games a day. Teams can have 3 day layoffs in hockey and can have home-away turn arounds of 1k miles back to back nights.

This makes writing the line in hockey tougher, and a few big bets can leave the bookie scrambling to fill the other side of the ledger. 20 cent lines leaves more room for error.

Also, who offered dimelines before matchbook (when it was avail in the US)? -aside from pinny-5D,No one, because there was no reason to. Books learned gamblers liked reduced juice and used that as the bonus in place of cash.

Now the market has thinned out for US players, and there is no need to give a dimeline. BO does for totals, but ML is a different beast..most any NHL total will be 5.5 on avg.