In all likelihood you will have many hundreds (if not thousands) of installed software titles across your organization. Each of these could have different versions installed as well as possibly being part of a suite (as opposed to stand-alone) or even named differently. Consequently, identifying and correctly inventorying all this software can be logistical nightmare, taking up considerable time and effort.
Some organizations will attempt to do this manually. Not only will this take a very long time, the results will be immediately out-of-date due to the dynamic nature of your IT estate. This led to many ITSM tools providing discovery and inventory services. Whilst the information these provide is useful for service management purposes, for software license optimization purposes, it is not nearly enough.
Issues with older ITAM tools
The same can be said for older ITAM tools and other products like Microsoft SCCM. The fact is that the initial discovery of what you have installed will pull up a long list of software names, editions and publishers.