May ask you why?

Is'nt that obvious?

It isn't obvious at all. There many reasons to prefer Nokia N900 over N9, or N9 over N900, Nokia N900 over Jolla, Jolla over N900, etc.

For example, with TOHKBDv2, Jolla is more N900-like than before. IMHO, Jolla + TOHKBDv2 has better physical keyboard than N900, N810 and Nokia 9500 Communicator. Only Psion Revo+ and 5MX have better keyboards.

Agreed.
But controversal are our opinions about the keyboards. Either the N900 one is definitely the best or I just did not get used to TOHKBD yet (but it doubles -at least- the user experience of the Jolla). But typing on N900 is way faster, especially with some -pssst, not working- keys on TOHKBD.

I cannot speak for TheoXD and I would not go as far as calling it complete garbage but, at least to anyone coming from the N900, Jolla definitely looks and feels like a toy.

TOHKBD2 is nice but it does not quite reproduce the N900 experience. The balance is wrong, for the starters. Too top heavy. It is also a bit on the big side (the whole Jolla, that is, not just the keyboard). On the positive side, TOHKBD2 has more buttons and resembles a real keyboard a bit more closely.

There are other issues that put Jolla in the toy category compared to the N900. Like the overall build quality and the quality of individual components (e.g. the camera). The lack of the FM radio (both RX and TX) and IR is seriously felt by at least some users. The sortiment of available apps for the N900 cannot compete with major platforms and yet it was much better 2 years after the release than Jolla's. Last but not least, developing for and on the N900 is a breeze compared to Jolla. I could find some 5 years old Qt source, copy it to my N900, type qmake and make and hey presto, it worked straight out of the box. Doing the same on a Jolla is a never ending struggle.

Ok, got it.. less hardware goodies, controversial kb (that you have to buy in addition to the phone) and OS not as good as maemo from developer's perspective.. anyway still not catching the "complete garbage" thing..

Btw, I was looking for a used Jolla or N9 as a backup phone to my N900... at this time only thing annoying me about my 5 year old N900 is microb getting older with new web standards and no good replacement in the near(?) future

Please create your own Jolla application and judge again. QML is way easier/productive frontend wise. Backend wise it can both be C++.

Old sources do not work on Sailfish because they are probably QWidget based, which are no longer supported in recent Qt versions. And most of the time you can forget about "working straight out of the box".
Not only is the aplication layout often desktop based, it also misses desired hildon widgets. I tried converting mediainfo-gui from existing QT widget sources on the N900, but was happy I restarted from scratch in the end. Porting apps in general (also Blackberry QML/cascades to Jolla QML/silica) is not that simple, else we would see that way more port. I think MartinK knows way more about these challenges

You are right about this. Especially security-wise.
BUT one example (I just found out by accident):
I have one online bank that now seems to use some newer/heavy JS. When they switched to that I could not do any banking anymore. Neither with N900, nor with N9 and also not with Jolla (all stock browser and all third-party). So I needed to switch on my tabl... [oops, not yet delivered and sure it wouldnt't work, too]. So start up desktop/laptop and waaaiit...
But then I just somehow disabled JS on desktop (NoScript) and I got the old web interface. Did the same (disable JS) on MicroB and the 6-year old beast is the only mobile allowing me to use that site!

If only There were a more linuxlike OS for N9500. I would charge it up

But even so I power its Symbian (and S40) up from time to time. Just for the fun of it!