Just because there have not been sightings of a particular animal or species, does not mean they do not exist. We have only discovered a limited number of animals. There are places that no human has ever been, so it is absolutely plausible to declare that some "extinct" species would still be alive.
I believe there must be other examples of animals that are still alive that we currently assume to be extinct. In areas that are very isolated and not populated by humans (such as the Tasmanian rainforest where the Tasmanian Tiger was recently discovered) animals can go undetected for decades. Although humans cover a lot of the planet there are still vast wildernesses such as the Amazon rainforest which could hide more non-extinct animals.
The world is big, not small. Entire planes go missing and we can't find them. There are many places left on earth where people don't go and where we don't know what happens. For this reason, there are species that we think are extinct that are surviving. They are doing so well surviving, they are keeping it a secret from humans.
People need to stop giving the Forteans media coverage until they actually find something. It seems every year or two they're in the media for "wanting to prove x cryptoid exists", "about to set out to find evidence of x cryptoid" or "very sure x cryptoid exists, they just need to find concrete evidence". Until they actually find anything this 'news' is about as simultaneously eye-grabbing and pointless as a Monty Python talking-head.