I don't think Stern is purposefully planning obsolescence. I think the surface mount components are simply cheaper for them to deal with, and a side benefit is the games will not last forever. I have mild hope that Stern is taking good notes when dealing with customers and collecting data to make smart design choices for the inevitable Spike 3 system. Spike 3 won't be easy to repair for most, but it will hopefully have some of the discovered design flaws addressed. Stern still has some interest in making sure the games last long enough that most people will not realize that their game is broken when it's collecting dust in a man cave.
This is an industry that has been transitioning away from a business model of operators routing these things for several years, making a nice ROI on the machine, and then simply sending it off to a dump when it stops being worth the effort/money to route. Pinball machines were designed to last only so many years for decades. Didn't some Williams/Bally guys say that things like clear coating the playfields likely hurt the company long term because it was such a significant boost to the service life of the machine?
Now new Stern games are going into private collections that will see a fraction of the number of plays, be coddled like babies, and being maintained by people that can't even operate a multimeter. The only thing they care about are the obvious cosmetic issues; they don't understand inherent engineering flaws when looking at a mess of wires and PCBs and couldn't care less because they have no interest in learning how to repair them, even if they were easy to field repair.
Stern will keep doing it because there are thousands of suckers out there buying these toys for themselves and not as commercial devices which have a much higher expectation on longevity and performance. Pinball machines are bought by the wealthy who don't care about spending $600 on some node boards vs spending $200 for a repair tech to fix issues on a WPC game. The Spike system was entirely designed around selling a couple of games to consumers and not operators. The writing was on the wall when it became the standard architecture for the entire product line.
Their private equity overlords will continue to push them to increase margins by decreasing BOM while raising prices. Stern will figure out where the tipping point is eventually, but until then they will continue to push forward to sell to the consumers with the deepest pockets and cause the the least amount of headaches. Home collectors simply don't request the accountability that operators require, and operators are being left behind as a result.