Relational database management systems e.g. Access and Oracle, are good at handling structured data where fields are less than 256 characters in length e.g. a person's name, address and date of birth. They allow you to store this information, but do not allow you to do indexed fast searches for words appearing within the free text. Rather than using an index to quickly find this information, relational systems must to do a slow sequential search through all the free text information.
Some relational engines offer hooks to free text engines.
However, these tend to be add on products that operate as a bridge between the relational engine and the free text engine. They do not offer true support for indexed free text data within the one database engine. Relational systems also have retrieval problems with fields less than 256 characters. In many cases, users will not know the leading words and want the flexibility to do these ad-hoc key word searches. Using wildcards instead of key words also greatly increases the probability of false matches.