What would you have them give you? Remember that competing alliances give pretty much the same perk. Given Silver is the lowest tier of elite status (above base) it only really serves as an incentive to get more - and given you can earn it with as little as 15k miles on TG I've no doubt there are Silvers galore out there. Yes, it might be nice to issue, for example, a "Star ALliance Lounge Guest Pass" valid for entry to one * lounge on a trip (to get a feel for the experience) but perhaps the pariticipating carriers would find this too costly in terms of people using lounges (and remember, the issuing carrier pays for each access of a partner lounge) and the numbers trying to get into lounges. Let's not forget that UA, AC, LH (the big 3) must have tens of thousands of lower level elites - it may be too costly to give out anything more - and anyway, they want you to go higher, so it makes sense to give not much for this level.

I also think the big incentive is for the host carrier to provide the perks - for example, UA Premiers get 25% mileage bonus, Y+ seating and 500 miler e-upgrades. I think TG gives an upgrade voucher, etc.

Incidently Silver isn't that bad. Heck, I got Op Opped twice as a UA*S (by UA, and TG).. I never got one as a UA*G at the 2 higher levels of the Mileage Plus program. Go figure!