The two bikes you reference are terrible examples. You've picked probably the lowest end tandem on the market. Why would you expect them to NOT weight a ton?

A tandem must sustain the weight, momentum, and pedaling of two riders. To make is safe enough to be sold to the average consumer, they simply HAVE to add material to the thing to make it meet safety standards. And even then, these are marginal at best.

Once you go up the quality ladder, this issue still applies - and in some ways, even more. Because higher-end bikes will be ridden harder and faster and longer, oftentimes with touring baggage attached. So the bike has to handle even more load, speed & stress. It is therefore far more expensive, especially considering the total lack of "economies of scale" the tandem segment experiences. However, the higher costs of the performance increases are totally worthwhile.

Three fundamental issues with tandems: beefier frame, more stout wheels, and oftentimes a third - and very heavy - drum brake. The very heavy Arai drum brake was always considered a crucial requirement for loaded tandems on long descents. Heavy but worth it. Life saving in some cases.

That said, and as others have mentioned, light tandems certainly exist. But they cost more than many small cars! Today's carbon fiber fabrication as it applies to bicycles, and specifically tandems, has proven a total winner on the strength-to-weight ratio basis.

"Light, strong, cheap, pick two!" applies here just so perfectly. If you're considering new tandems under $2k MSRP, you're getting heavy, heavy, HEAVY!