It could either have been disabled by you, using the isELIgnored page directive attribute or the <el-ignored> element in the DD ( web.xml ).
The more probable cause is that you're using the DTD for specification 2.3 and not 2.4. With the Servlet specification 2.3, EL is disabled by default.
Also, keep in mind that with the JSTL 1.0, you could use the EL as part of the tags, like <c ut> ( using the RT version of the library ) but not anywhere else in the page. JSTL 1.1 is meant for the JSP specification 2.0.