Software does not go away. It may be discontinued though. So is free software occasionally.
Do you take over development of all free software you use which is discontinued? Well, fine for you, but I wouldn't even have the time for that.
Either I'd stick with the last version or I'll look for an alternative. No matter if the particular software is free or not. Sorry, but if I need a new hammer, I'll buy one instead of building one myself. Again: For me, a tool is primarily a tool and nothing else.
Congratulations. I don't need it.
... with the risk being that you might need to search for an alternative one day? Alright.
What if your work required something that is very specific and the proprietary alternatives didn't provide what you need?
At least with Free Software, if the software doesn't do what I need it to do, I could fill the gap and code it myself, or hire someone else to do it for me.
And no, I don't take over when a Free Software project is discontinued, other people usually do that with forks and such. But I would if I have to.
My point is that it's just easier to get screwed with proprietary software.
... with "getting screwed" meaning "having to change one day in the very far future". Alright.
I find it curious how you completely skip the malware and privacy implications of using proprietary software. They are a rather big part of "getting screwed" by it, on top of possibly losing the ability to use it any time.
Many of them call home. Many of them track you without even informing you. And this is just the benign part of them - more nefarious proprietary software outright does anything it can.
Or, to use a web example, if you use some forum you don't have the source to (say, vbulletin), how can you know they properly hash the users' passwords?