There are some devices such as step up converters that if you connect the power supply reversely it will burn, also some ICs such as ic555. my question is >> why the manufacturer doesn't use simply a diode for reverse current protection?
Such a diode would
- add to the size of the chip and hence to the price
- drop some voltage, hence the chip would have less or you would have to supply more
Nearly 99.99% of the chips are bought by professionals, to be included in a carefully designed circuit. If that circuit needs reverse-polarity protection such protection is added at that (circuit) level, in a way that is appropriate for the product (diode, fuse/crowbar, asymmetric connectors, etc). Putting such a protection in each and every chip would be bad engineering.
Or see it this way: chip are not designed and optimized for the careless hobbyist, but for the large-volume buyer. Such buyers generally do not want to pay (in price or performance) for things that are not needed in a well-engineered and well-produced product.