I mained lance in 3U and 4U too. You have a 3-attack limit (except that the shield bash can precede it and IIRC the joust charge can follow it). The counter resets the combo, but can't be done after the 3rd attack of a combo AND it counts as the 1st attack of the new combo. So the most you can do is first poke, second poke, counter (3rd attack AND 1st attack of new combo), poke (2nd attack of the new combo), counter (3rd attack AND 1st attack of new combo), and so on.
That's how it was in 3U and 4U. It was an infinite combo, just not as good as having the option to do another poke between the counters like they let you do in Tri.
I just booted up MH4G and wow, yeah, how did I not notice that? I guess I've been used to the Tri combo and never thought of chaining before the 3rd. Interesting.
It makes sense since the Tri infinite was too good IMO. The damage output and the relative safety of the counter meant you could poke stuff for days. I miss it but whatevs.
The question is if it's worth chaining counters or just using the 3rd multi-hit attack for damage.