The fact the Switch 1 will sell at or close to 1 million in Japan this year, and Worldwide being at least 2 million this system won't get discontinued until 2028 at the earliest. With PS and Xbox prices being so high the Switch 1 family are the cheapest modern consoles you can buy so it makes sense it still sells. Remember the 3DS sold an additional 10 million after the Switch released before it was discontinued due to it's low price.

Top 30: https://nintendoeverything.com/famitsu-softwaresales-4-13-26-4-19-26-top-30/

1. [NSW] Tomodachi Life: Living the Dream – 565,405 / NEW
2. [PS5] Pragmata – 36,470 / NEW
3. [NS2] Pokemon Pokopia – 19,096 / 910,005
4. [NS2] Mario Kart World – 5,130 / 2,900,842
5. [NSW] Minecraft – 3,550 / 4,190,151
6. [NSW] Animal Crossing: New Horizons – 3,538 / 8,423,202
7. [NSW] Doraemon Dorayaki Shop Story – 3,299 / NEW
8. [NS2] Animal Crossing: New Horizons – Nintendo Switch 2 Edition – 3,067 / 104,917
9. [NSW] Nintendo Switch Sports – 2,459 / 1,720,506
10. [NSW] Pokemon FireRed/LeafGreen (Download Card) – 2,169 / 20,218
11. [NS2] Xenoblade Chronicles X: Definitive Edition – Nintendo Switch 2 Edition – 2,041 / NEW
12. [NSW] Super Smash Bros. Ultimate – 2,022 / 5,901,855
13. [PS5] Crimson Desert – 1,955 / 44,588
14. [NS2] Super Mario Bros. Wonder – Nintendo Switch 2 Edition + Meetup in Bellabel Park – 1,965 / 18,767
15. [NSW] Momotaro Dentetsu 2 – 1,836 / 340,540
16. [NSW] Mario Kart 8 Deluxe – 1,819 / 6,566,060
17. [NS2] Pokemon Legends: Z-A – Nintendo Switch 2 Edition – 1,814 / 1,114,440
18. [NS2] Resident Evil Requiem – 1,808 / 56,461
19. [NSW] Pokemon Legends: Z-A – 1,784 / 1,638,151
20. [NS2] Mario Tennis Fever – 1,765 / 103,355
21. [NS2] Monster Hunter Stories 3 – 1,729 / 62,066
22. [NSW] Super Mario Galaxy + Super Mario Galaxy 2 – 1,655 / 166,384
23. [NS2] Super Mario Party Jamboree – Nintendo Switch 2 Edition + Jamboree TV – 1,624 / 187,737
24. [NSW] Super Mario Party Jamboree – 1,512 / 1,503,225
25. [NS2] Momotaro Dentetsu 2 – Nintendo Switch 2 Edition – 1,467 / 293,952
26. [PS5] Resident Evil Requiem – 1,412 / 207,836
27. [NSW] Dragon Quest 7 Reimagined – 1,378 / 249,721
28. [NSW] Splatoon 3 – 1,207 / 4,531,027
29. [NSW] Clubhouse Games: 51 Worldwide Classics – 1,170 / 1,493,029
30. [NS2] Kirby Air Riders – 1,091 / 521,308

NS1 - 15
NS2 - 12
PS5 - 3

Switch version of RE Requiem outsold the PS5 version again lol, and the Switch 2 physical version of Pragmata was delayed and will release in Japan on April 24

Not surprising considering most of PS5 sold are digital editions. Even tge pro doesn't come with disc drive 

On a weekly basis now yes, but unless I'm reading the OP wrong, of the 7.5m PS5s sold in Japan, 5.9m are the base version which has a disc drive, so the large majority of its install base.

Yes and that 1st week showed it. After that it's pretty much it and whatever sold come from the new hardware sold weekly. We'll most of it

Software sales aren't just comprised of new console owners, pre-existing owners still buy games. Maybe word of mouth convinced them to give it a try months down the line, or they were too busy with other stuff or didn't have enough spare change when it first came out.

After the first few weeks a high percentage of software sales are from new hardware owners. And PS5 digital software sales are higher than Switch 2 too. Too bad we don't know the digital sales in Japan 

is there any actual data on what share of sales are from new owners? 

Digital ratios are higher on PS, but there's also a disc drive add on for the PS5 Pro and Digital Edition isn't there, so the total physical-enabled install base for Requiem to sell to will be higher than the 5.9m base PS5s in the wild.

I just looked at the chart. Requiem sold 1.8k on Switch 2 and 1.4k on PS5. You don't think most of these sales are from new hardware owners? Like 1k out of the 42k Switch 2 sold this week ?