I think combo/finishers is something a lot of people easily miss as it's not very well explained by game mechanics plus the nature of the game kinda 'hides' it from a lot of peoples natural play.
A lot of players in the game are ultimately solo players. Even some who are members of guilds, will still prefer to play entirely on their own rather than band up. Certainly, the content of general game play (hearts etc) doesn't encourage team play. Why would people? There's more profit in dungeons than most open world content.
When they reach end-game, they may start dungeoneering or going for fractals. They'll start trying to hone their own build, but they'll end up playing with PuGs. Their main focus will be what is their primary concern - raw dps, DoT, survivability etc. For their own character, without any consideration for other classes. Many at this stage of game play are still unaware what other classes are capable of, and still the combo field thing has never been used all through their game experience right up to this point.
Eventually they'll progress, get a feel for their class properly, and even roll some alts and get a feel for them. But even so, it's still a largely solo experience.
They may eventually even enter WvW, and maybe they'll even be around at the right time an organised commander is playing. They won't get why they want static fields and blast finishers before rushing a mob still (surely that's a waste? surely you'd want to static field the enemy to CC them?) - it doesn't connect.
Then they find out about this dragon thing that people zerg. At least, that's what it looks like to an outsider. People explain things, but people don't quite get what is where until they actually try it a few times. Yet still right up to this point, in their entire game experience, they've still not twigged what a combo field is.
Even though they may have seen things like "area might", they probably still haven't properly twigged how to create that effect, just that it sometimes happens if two people happen to do some things at the same time, but they don't know what.
I had players in my GW1 guild that were there from the start. While the most of us were theorycrafting how to clear the Domain of Anguish as a 3 man team, others in our guild just soloed away.
Towards the very late game as guild wars 2 approached, they actually reached out to us and asked for help. We took them on basic missions and just watched their builds fly by. Some very confused setups. They had no idea how to make the skills synergize on their own bar, let alone any sort of synergy with others.
This is the big problem regarding combo fields really. Many people don't get them because for the large part, they've spent the entire game in isolation and don't really understand the full extent of what is possible in the entire game.
Most combo field triggers are AoE, which is the easiest kind of skill to target when in a big blob - place a thing on the ground, it's gonna hit something. Right? Some people will just mindlessly spam their bar, as their early gameplay experience hasn't explained any mechanic properly. 1 Does damage. 2 does damage, 3 does a thing, 4 does damage. Spam the skills! 1,2,3,4,5, repeat.
So it doesn't surprise me that people will go right up to tequatl and just unload their entire bar, wrong combo fields and all. They don't have a mastery of their own build, nor any knowledge of a combo field, and sadly, the game itself has promoted this kind of behaviour for all except those that really *really* want to get ahead in the game.
However, I think the people who attend the events are listening and are learning, but there's always going to be new faces who haven't yet been shown any ropes and will make huge mistakes.