Please do not write below the line

Likeliest situation is all their stationary destined for send outs have the line; and in situations where the line serves no purpose it does no harm to leave it: so there is little use in having additional process around completely blank stock.

They could have told him that though if it's the case, and the mystery would be solved. But there obviously wasn't any desire (or more charitably - time) on their end to really look into the reasoning or even understand the question.

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Edit: I will share what I think is a nice a little counterpoint story here, from a business that is clearly still interested in understanding. I sent Lego an email a while ago:

  I'm just wondering if you're able to tell me what the
  tune is that the Lego Primo musical camel plays in set
  number 2007. It's a set from 1998. We have the camel and
  it plays a nice tune, but no-one seems to know what it is! 

They replied a day later:

  Thanks for getting in touch with us. 

  This is a really really really and I mean really interesting
  question you got there for us. I have checked with all the
  resources I have and come to a possible conclusion.

  The Musical Camel – which in Denmark actually is called
  ‘PRIMO Dromedar'. 1st theory is that, One DUPLO-designer
  says that the melody was composed by the designer that
  created the camel but no one remembers the name who created
  the Musical Camel. Another thing is, one of the engineer once
  had a musical box that had the same melody but he is no
  longer with us anymore and cannot provide us the answer.

  I am so sorry that, at the end of the day I cannot provide
  you with any name to the title. But I hope the facts can
  make a good story for you to tell your friends.

The thing is, Lego is a "nice" company, and they care about their image. Answering obscure question the best they can goes a long way, people will be more than willing to share their anecdote. That's great publicity, and all you need are a few guys answering emails, most of them are likely to be copy-pasted for the most part, people are not that original. And if you get a truly original question, it may take a bit more time, but the impact will be greater, and I am sure employees have great fun finding these bits of trivia.

TV licensing on the other hand is "evil". They are in the business of collecting a tax that many people see as unfair, and prosecute those who don't pay. Even if their actions are fully justified, they won't make your life better, it is simply not their job. Even if they are genuinely nice in their communication, it won't change the fact that their are after your money and have to be forceful sometimes, and everything will be seen through these lens, so they might just as well assume their evilness.

More importantly, they don't need to be nice and/or care to be successful.

Businesses are nice because they have to compete for customers, and that is easier if you're viewed as nice.

TV Licensing is a monopoly, they can have the worst customer service on earth, and that won't affect their revenue by much. There's just nowhere else to switch to.

This is also the reason why many government / publicly-run systems are so unfriendly and have such terrible UX. It's not like you can apply for benefits somewhere else (and the government would actually be very happy if you could!) , so nobody cares if the application is fifty pages and requires you to put in the same personal details 5 times.

To add insult to injury, there are no shareholders that demand the metrics to go up, so nobody has any incentive to optimize anything.