The 'missing' spells are not available for individual purchase because they are already freely available
These spells can be found in both the Elemental Evil Player's Companion (EEPC) and Xanathar's Guide to Everything (XGTE).
The spells that are included in EEPC are freely available to all - that pdf is officially a free download.
On DnD Beyond you can buy access to an entire sourcebook or you can buy items of content from that sourcebook piecemeal. To this end, the page you have linked to contains a list of all the spells you can purchase from XGTE as individual purchases.
The spells in the EEPC are all reprinted in XGTE (with a few tweaks) but they are not listed as individual purchase options on DnD Beyond becuase they are already freely available to all users - like the basic rules.
The list of spells that you can see on the linked page is thus not a complete list of all spells in XGTE - it's just the list of spells that you don't already have free access to.
For comparison of this phenomena elsewhere, see the purchase page for the PHB. No Races are available to purchase and the only available Subraces to purchase separately are Dark Elf and Forest Gnome - while the actual book contains 9 different races + subraces to go with most of them.
To access all of the free content on DnD Beyond, including the 'missing' spells just create a free account - no purchase necessary, though that won't give you access to the official Artificer subclasses - which are behind a paywall.
In summary, the list of individual purchases available, from within a sourcebook, is not an accurate summary of that book's contents, and should not be treated as such.
Note: You are not looking at the latest version of the Artificer, which has now been published offically, and has over time gone through many changes.