They're almost certainly working on ports or remakes of remasters of multiple Dragon Quest games. They released a major remake of DQ10 a little over a year ago. They are releasing DQ3R soon. Probably a localization of the 10 remake this FY. Have semi-announced 1/2 following 3R. Shit takes time though and ports of games native to weird aspect ratios aren't easy. Ports of stuff outside of the widespread third-party engines are nowhere remotely as easy as some people seem to think. Like, people are off by an order of magnitude in cost here, and difficulty porting stuff from that era is why they bit the bullet to do full remakes in Unity for the Final Fantasy PR games and are likely doing the same for Chrono Trigger.
At this point Square Enix is doing probably the most non-emulation ports of old games of any publisher. But that takes effort and expecting them to do 15 per year instead of like 5-10 is just wildly unreasonable expectations. Most remakes and remasters going forward are going to be extensive overhauls to put the games into Unreal or Unity as much as possible to keep long term maintenance and porting costs down.
If they've done the work to port 1-3 to Switch, then the most labour intensive work is already complete (getting the framework the mobile games run on operating on the weakest target hardware). There is no good reason, aside from what is becoming typical SE production mismanagement, for rudimentary RPGs to be delivered in a piecemeal bloc of 3 games to only one system, followed by 4 1/2 years of nothing. Whatever is going on internally, it appears completely arbitrary and unaccountable in the real world, which is probably why the series' producer has been shuffled elsewhere.
Nobody is demanding 15 ports per year. They're comparing SE's stated intention of "expanding Dragon Quest in the West" pre-DQXI against their actions to date, and against other publishers that do seem able to walk and chew gum at the same time when it comes to multiplatform strategy and availability of legacy software. SE placing hopes in a delayed international release of DQX (assuming it happens) would be completely irrational, because:
1) It is yet another platform-exclusive release after the previous mainline game's release strategy of "buy a PS4 for this, or actually a 3DS, but also Switch at some point, or Steam because we want to expand in the West, and here's the Switch version now with additional content, ok now here's the Xbox version of the Switch release and also we've replaced the Steam version with the version that adds stuff but looks worse, buy it again with no discount". Why is DQX, which is trivially easy to run and even has a PC client, Switch exclusive? Self-imposed Square-Enix reasons - probably good reasons, since the basis for the game is a Wii MMO, but why should the general consumer care? They're drowning in quality anime/JRPGs.
2) The Switch is in its last year - the sales potential of a late offline port of a 3rd party former Wii MMO is frankly at its lowest possible ebb. It can only succeed on its merits and the current strength of the brand internationally (way below it's hypothetical ceiling), and plenty of great games underperform on hardware that's on its way out.
Much like Monster Hunter and Like a Dragon before their breakout games, I believe DQ can reach a way bigger audience than it currently reaches. However, so far SE have squandered the closest they've had to a Monster Hunter World/Yakuza 0 moment with DQXI, and have repeated similar mistakes they've made with their other pillars. It is not "wildly unreasonable" for a general customer to see what is supposedly a 3rd party multiplatform series, take an interest, and go from there to buying other games in the series with minimal friction. Capcom do this with multiple generations of complex 3D action games and as a result have insane long-tail sales, yet SE can't do this with 2D tile-based RPGs that have already been moved onto a modern API through the phone releases.