I come across a lot of campaigns in Adplexity which are running worldwide in English language. My question is that how they can become profitable running 1 campaign in English language? If yes, what kind of verticals work?

Usually the offer is international and if you target worldwide in most networks you get cheaper clicks.
So probably they are just bidding the minimum price and that makes up for the lower converting geos.
That is a great question and similar to ones I asked myself when I first started with natives + adplexity.
There's several answers:
1) What you see in Adplexity- while incredibly valuable- isn't always a good reflection of volume. Some networks' ads show up way more (Outbrain, Revcontent) compared to their actual volume, and some way less (Taboola).
2) The volume of those two campaigns in your screenshot is likely not a reflection of their overall daily spend so much as it is their distribution: i.e. total countries those ads appear in X device types. In this vein, I once had an INTL campaign on Revcontent that was literally spending under 50$ a day, yet looked on Adplexity like it was the biggest native campaign in the world, just because I had selected a ton of geo's on the targeting page. Again, that's because Adplexity's spiders can't really scrape to determine total ad spend, only what geo's plus devices the ads appear in.
3) Different networks allow for different targeting. On Revcontent you can target tons of countries but also select to only target people whose browser's are set to 'English'. This is actually really good traffic typically, because you get a lot of expats and servicepeople stationed overseas and so on who typically have more money than do the locals in those countries.
I've never used Contend.ad so I can only speak to Revcontent, but targeting lots of geo's + English is a great strategy. It's not likely to yield a ton of volume though, as you would get targeting a bunch of countries on Taboola or Outbrain.
I often run parallel campaigns on Revcontent where Campaign A is just targeting US and has the higher bids, and Campaign B is identical but targets the US + lots of other geo's, with much lower bids. Interestingly you'll still often get a decent amount of US traffic anyway.
Finally... to answer your question about whether you can make such campaigns profitable, the answer is obviously 'yes', however profit is just one component of it- the other factor is volume. On some of the smaller native networks you might be able to get a good profitable campaign going in one or more of the intl geo's, but the volume might be limited, thus potentially not worth the time investment. That depends on each person's unique situation/funds/cost of living/etc though.
Love the profile name by the way @melkorglaurung!
Just 2 more points I'd like to add:
1. Quite a few people are using EN ads and then send the traffic to a localized LP, not sure why, but I've seen this many times already. Especially with simple copy, that is kinda universal and easy to understand.
2. You could be looking at failed campaigns that people keep on copying from each other, hoping that it's gonna work. Part of it could also be campaigns managed by bigger networks that have private deals with traffic networks that sell them "remnant" traffic for cheap. In such cases they sometimes use a generic ad to be shown to multiple GEOs.
With VDSP where you can target multiple networks (RevContent, MGID, Nativo, Smaato, etc.), you can ask your AM for some insights on the top performing GEOs for a specific offer - just provide your AM with the link and your KPIs - and your rep will be happy to recommend a few top networks along with the countries.
Stop spamming your DSP.