I don't have time to look it up but I'm pretty sure your math is way off. First party software sales are the second most profitable thing they have, behind network (PS plus etc)
I double checked the numbers:
On PS they sold this FY 43.9M 1st party games, which are 14.47% of the total 303.2M game sold for their consoles this FY. Please notice it doesn't include add-ons (microtransactions, DLC, season passes, where 3rd party makes a better job than them), these are games sold.
So this is a 14.47% of Physical Software+Digital Sofware, which added are 699,789M Yen, a 14.47% of it is 101255.13M Yen (you can compare it below vs their other segments), which is $796.44M (+ 1st party add-on content) made by 1st party games on PS.
On PC they made an additional $80M, a 10% of what they did on PS. What they did with 1st party this FY on console+PC not counting add-ons is $866.44M, which is a 4.02% of what their gaming division made in revenue this FY: 2739.8B Yen ($21.55B). This is not counting mobile gaming, which they have under Sony Music and it's like another Billion dollars or so.
I don't disagree with this in general, but even releasing pc games later technically erodes this, I've already seen many people here say they would just wait.
Most PC gamers (or at least a bigger percentage than in console) wait for good discounts for games that release day one on PC, so I assume to wait isn't an issue for them.
For Sony, 1st party PS+PC sales provide 4% of their revenue, which is a small portion of their business. So for them is better to keep them at least some years exclusive for their console to pump all the other related business that players pay for when they got the console to play these 1st party games there: hardware, accesories, services and more importantly: other 1st party and specially 3rd party games (who pay their 30% cut to Sony).
Compare apples to apples, we aren't comparing the cost of one game vs two, we are comparing two version of the same game being developed either simultaneously or after the fact. It's always going to be far cheaper to develop both versions at the same time. Always.
To have a huge team developing for a single platform and later a small team porting it to another platform once is completed is cheaper than to have a huge team developing the game for the two platforms at the same time.
First the amount of devkits, licenses and so on. Second, to design, implement and test everything to run optimally everywhere. A lot of extra time and money would go into this and the games would be worse because they would have to make sure the game is complete and runs well in the least common denominator, which would be low end PCs with HDD.
Consider that game development is a 'chaos' full of iterations, where tons of things get experimented, tested, iterated, changed, tweaked, optimized, fixed, added or removed. It isn't the same to verify it runs well every iteration of every one of these things in a single device than in 5. Let's say a specific game mechanic or game stage gets tested and changed a ton of times during development and must be tested it works, looks and runs well on every device. So lowering the amount of devices lowers a lot the development.
When making the port of a game that already has been released, all these features, mechanics, stages and so on won't change. Meaning that the work and const involded on bringing the game to this machine would be way lower when making a port of an already completed game. And this is only counting the gamedev part.
It's not going to take that long, and they really need some day and date stuff to drive it's success.
They don't need day one games on PC to be way more successful than they are now right now.
Ports of old games is enough for them, as I explained above this FY PC ports made a 10% of revenue of what they did in console. And being ports, with a way higher ROI. If instead of $80M on PC they'd have made the $300M they expect for the current FY it would have been a 30% of what their 1st party games made in console.
And what is more important for them, late PC ports don't break their success on console, which having day one games on PC could. Because as in Xbox, it would mean many players who are both in PC and Xbox would stop buying the console and would keep in PC. For MS this is fine because their main business is related with Windows and cloud stuff, not the console or their 1st party games. But would be a big issue for Sony because their main business is the console, not PC or their 1st party games.