It is small and no antenna kan be seen. Many users are willing to pay extra to get rid of the antenna that get caught in clothes etc.
Designers are glad to be free to model a phone without the constraints of an antenna on top.
Also the emerging use of fractal antennas and compact helix antennas are contributing to the trend. And to make it worse, we already have indications that SAR is not the best measure when compared to complaints from users. Also, SARs that are computed must be computed from both E and H near fields to be valid. As for actual measurements, the best thing is to nag, beg and lure the customer organisations to fund and publish measurements on all phones on the market.