Why has the rest of the world gone after delta wings while not the USA?
The Gripen and Eurofighter are canards with a delta wing (as is the J-37 Viggen). This, coupled with relaxed stability, gives the first two unmatched maneuverability, and good transsonic and short-field performance. While the Viggen is a stable design, it too has very good short-field performance.

The Mirage III (and the F-102, F-106, B-58, J-35 Draken and Concorde) were first-generation Deltas from the mid-1950s which were optimized for supersonic speed. By using a highly swept delta wing, low supersonic drag could be combined with short take-off and landing distances.

So it is not true that the US "never went after delta wings"; they just outgrew that configuration when they shifted their priorities away from high supersonic performance. 

Note that the more modern Mirage F1 is an unstable conventional configuration while the last Dassault design is also an unstable canard.

Regarding the Tejas: It is designed for the specific requirements of the Indian Air Force. One of the unusual design requirements was the low vulnerability to bird strikes, because Indian airfields have a high birdstrike rate. Therefore, no leading edge devices were allowed, and to give the Tejas still a respectable short-field performance, a delta wing was the best choice. Full disclosure: This was actually the requirement which led to the LCA having a delta wing, and the Tejas, which resulted from the LCA, does have leading edge flaps after all.