LTE penetration is still a huge issue. Then there's the question of band support (different carriers use different LTE bands - not all mobile data devices support all bands).
There're two reasons why LTE isn't a panacea to cell standards bifurcation and modern cell phones still require fall-back data radios that support EVDO, HSPA, etc.
They can now. Before we had (and on iPhone still have?) different models to handle different carriers. That's not a good UX for customers, especially as computers are still not at the commodity level that phones and tablets are (refresh purchases are 3+ years apart).
There're two reasons why LTE isn't a panacea to cell standards bifurcation and modern cell phones still require fall-back data radios that support EVDO, HSPA, etc.