It's Because They Are Telling You Something About Your Code; It's Buggy!!!!
Worse than people of turning 'strict' are the people who don't understand 'strict' or 'warnings'. People who think that 'strict' or 'warnings' issueing warnings conclude the code is 'buggy' don't understand 'strict' or 'warnings'. And are hence not qualified to use it.
Yes, it's good to turn on strictness. It's good to turn on warnings. But it's only useful if you understand the messages it issues. Its messages indicate the code may have a problem spot. But it doesn't have to be, and perl may be wrong to. The conclusion that "oh, it gives messages under strict/warnings, hence the code is buggy" is too shortsighted, and a signal of poor understanding of Perl.
Note that I'm not claiming the code you refer to doesn't have bugs - it probably has. I'm just ranting about your generalisation.