I presume by older languages, you mean Java (1995), Python (1991), C++ (1985), PHP (1995), Ruby (1995), Perl (1987), JavaScript (1995), C (1972), R (1993), C# (2000).
Older languages are proven and reliable. They’re trusted.
Older languages have rich ecosystems and large user communities.
Older languages have large legacies of software that must be maintained which means…
Older languages have more job opportunities. According to Indeed.com:
Java – 60,977 job postings for the United States
Python – 48,346
JavaScript – 44,131
C++ – 32,230
C# – 26,553
Ruby – 17,975
Perl – 14,019
PHP – 10,313
New languages have job postings of under 1,000.
New languages do not usually offer enough benefits to offset all of the above advantages. They’re untested and not trusted.
Also, no programming language is perfect. New languages have their issues, too.