The reason is simple. Because their techniques may not be solid enough yet. In the following short clip, you can see that the guy used the same SC "bear hug, outer hook" technique twice within 14 second. It proves that he did not use that move by accident without planing. Also he used the Longfist roundhouse kick, side kick combo to enter and finished with a TCMA SC throw, it indicated that he did not fight like a kickboxer (not sure round house kick, side kick combo is a common move used in kickboxing) or MMA guy (not sure bear hug outer hook is a common move used in MMA - also please notice that the hooking on opponent's "back leg" is very TCMA). This is a full contact Sanda/Sanshou fight and his opponent was very strong.
http://johnswang.com/Sanshou_6.wmv