Is there a reason why some institutions don't configure a rDNS in their website?

When I did nslookup from some random site it threw me an IP address, when I use that IP address for another nslookup it returns this *** UnKnown can't find 171.161.206.100: Non-existent domain

Here's an example in case I didn't make it clear

C:\Users\Hyper>nslookup www.bankofamerica.com

Server: UnKnown

Address: 192.168.1.1

​

Non-authoritative answer:

Name: wwwui.ecglb.bac.com

Address: 171.161.206.100

Aliases: www.bankofamerica.com

​

When I do it with the IP address given

​

C:\Users\Hyper>nslookup 171.161.206.100

Server: UnKnown

Address: 192.168.1.1

​

*** UnKnown can't find 171.161.206.100: Non-existent domain

​

I asked the reason of this error and I was told that there was no rDNS configuration, I have noticed that I get the same error in rDNS look up in various bank and institutions webpages, seems like a pattern here, is there a security reason of why not configuring rDNS? or is it just a weird coincidence?