Their local store surviving and expanding their operation during these 3 years could be enough of a benefit.
The store can plan for what they'll do 3 years later, so progressively injecting IKEA competitors in the mix and getting people to know the other options could lead to a durable business. Especially if IKEA loses enough sales that they'd want to keep selling their goods in third party stores to keep shelf space from competition.
To get out of the metaphor: if alternative app stores become big enough to thrive on their own from this initiative, app makers will keep pushing their apps other there. In particular this whole scheme assumes some level of compatibility, so the burden should be light enough.
