Kaokai Chor.Hapayak (120lbs,RED) vs Lukkwan Sor.Jor.Waopadriew (120lbs,BLUE). Kaokai and Lukkwan fight on the "RUAMPHONKONPEDRIEW" promotion at the New Lumpini Stadium, Bangkok. Full HD, Filmed and edited by Timo Ruge
In the first round or two they go relatively slow & easy so they can warm up and feel out their opponent. Then later rounds they keep upping the intensity.
You obviously asked this question a long time ago, but thought I'd follow up a bit. The first response is one reason. Additionally, Muay Thai is scored differently than other combat sports. Landed kicks and knees count much more than punches or elbows. Punches and elbows only score if they show visible damage. There isn't much point to continuing a flurry against a guy covering up. Also, last kick counts. If I blast you with a leg kick, stay in range and you blast me back, that exchange scores for you, not me. So typically you'll see someone back off and reset after landing a clean kick or knee. And then as the above comment stated, that's just kind of the way Muay Thai is.