Actually I suggest it is not at all made clear unless you go to the website. Announcements on stations and trains don’t mention anything other than people who see anything should contact a member of staff or text the BTP. While I am sure everyone knows 999 can be used for emergencies, the implication is that on the railway the first course of action is BTP.
Well they give an alternative - speak to a member of staff. The fact this is first suggests it's their preference. As 61016 is not for emergencies, it should not matter too much if you have to wait until you arrive in a station before speaking to someone. I don't know how many people have phones that can't text BTP, but there's a good chance that on most services someone else will also report the incident. I doubt there are many crimes going unreported as a result of people's inability to send a text message.
In an ideal world, texting BTP would be free. I think the fact that it's treated as a charged-for number is just an impact of the way these short text numbers work, not a conspiracy theory or an attempt to generate profit or dissuade people from helping the police.
I have a friend who handles ambulance service 999 calls. He says the biggest problem is people who are panicking, and are therefore unable to answer the questions clearly so they don't know what help to send, or where to send it to. I can only imagine how difficult this would be to deal with if you only have a text message, especially if the person who sent the text then doesn't/can't answer their phone.
As an aside he also dislikes calls that are connected from a mobile via a different network (when the phone's own network doesn't have a signal). The problem with these calls is that if they drop off, they cannot contact the caller - they can't call them back as they know the number but it has no signal.
To make it easy to report problems? I won't bother ringing them on their non-emergency line to report an issue but I'll happily text them as that's easier and more convenient for me. I'm not quite sure what the issue is with them having multiple ways of reporting issues? If you don't want to use it no-one is forcing you to and you can email them or ring them on their non-emergency number. Everyone's happy then as they have ways of reaching them that work best in their situation?
It's a bit like the TOCs - most of them are very good at handling queries via Twitter. Of course not everyone uses Twitter, and those that don't can ring National Rail Enquiries. But for a large number of customers, and for the TOC, Twitter is a useful and efficient channel and it would be mad not to make use of it.