It is more simple to attract money on IEO that on ICO. But a fully regulated STO is much more better then IEO.
It is necessary to get approval of financial regulator to conduct a fully regulated STO. That is why STO is so rare.
Now financial regulators do not have a big practice with STO. There are a few STO and many businesses do not hurry to tokenize their assets.
In many countries cryptocurrency is not regulated. Even in countries where cryptocurrency is regulated financial regulator does not have enough practice of conduction STO.