> even though new lang. were developed.?
Carpenters don't agonise over why everyone still uses axes, following the invention of the chisel and the saw.
They're all just tools in the tool box, and it's up to you to use the most appropriate tool(s) for the job. Any sufficiently complex programming task will almost certainly make use of several languages.
Cobol and Fortran are both much older than C, and there's no sign of them being dislodged from their particular niches any-time soon. Both are regularly updated to bring in new features, improve the language or whatever.