The other Cleric subclasses you are referring to is not part of the Dungeons and Dragons 5th Edition SRD and will need to be unlocked from the marketplace before you can use it on D&D Beyond.
You may also purchase individual races, subclasses, feats & magic items from the marketplace - should you later wish to purchase the sourcebook that they came from, any such individual purchases are fully discounted from the price of the sourcebook. You are also welcome to create your own content using the D&D Beyond homebrew tools.
Why can I only chose life domain in the class section.
Hello Zintra!
The other Cleric subclasses you are referring to is not part of the Dungeons and Dragons 5th Edition SRD and will need to be unlocked from the marketplace before you can use it on D&D Beyond.
D&D Beyond can be used for free and contains information from the following "free to use" sources published by Wizards of the Coast: D&D 5th edition SRD, D&D 5th edition Basic Rules, and Elemental Evil Companion.
Content from other sources, such as the Player's Handbook, Dungeon Master's Guide, or Monster Manual, will need to be purchased from the Marketplace or accessed via another user sharing content with you via their Master Tier Subscription.
You may also purchase individual races, subclasses, feats & magic items from the marketplace - should you later wish to purchase the sourcebook that they came from, any such individual purchases are fully discounted from the price of the sourcebook. You are also welcome to create your own content using the D&D Beyond homebrew tools.
Hope that helps!
Short answer: Because the life domain is the only free one and you haven't bought the others.