Now secure tokens that are backed up by real assets are very rare. That is why STO where secure tokens are sold much more better than ICO or IEO.
It happens because cryptocurrency startups usually do not have assets in property which they can tokenize to issue secure tokens.
When crytpocurrency startups appear usually it has nothing besides idea. And it needs money for the realization of its ideas. That is why project conducts IEO.
Now a lot of investors prefer to invest money only in products that have a ready MVP. So before conduction of IEO somethings must be done.