For Eurobonus at least I guess the registration process is due to technical reason. They will do a database search for all the flights concerned (a lot) for the FF numbers registered only.
The flown segments database, which is linked to ticketing etc, is huge.

As a general note on customized offers - SAS knows that some would appreciate special offers (eg. "Hi, as you fly a lot on short notice to ZRH we would like to offer you bla bla") while others would feel offended and react negative.
Also authorities in Sweden is monitoring this - food chains in Sweden for instance have been prohibited from using their receipt databases in too much detail and have to divide customers in very broad groups.

Still, I know that the main reason for a loyalty program is not to give out points - it is just the incentive to get the customers to register so that they can get all the details of your travel pattern. And I am sure SAS would like to use all this data more - but they are afraid that people will react negative if they realize the airline is actually using the pesonal data for marketing.
You can be sure they are using it for other internal purposes - such as revenue management (is there groups of travellers - and how big is that group - that notoriously buys the most expensive tickets the day before travel or not? etc etc)