Why?

As news have it (in Russian) Trump wants to see Russia, India, Australia and South Korea at what used to be G-7 meeting some time in the future (in Russian). As you may have noticed already, one entity which is conspicuously absent from this is the largest, by far, economy in the world, which is China. This is not to mentio0n that the fact that Trump's desires mean absolutely nothing for Russia, who has a committed relations with China. Trump also has to understand that Russia was in decoupling mode with Europe for a few years no. Sure, selling Russian energy to Europe is important, so is important to sell finished and agricultural products, but here is a short view of what Russian-European trade relations look like today:

Russia is the EU's fifth largest trading partner and the EU is Russia's largest trading partner, with a two-way trade in goods value of €232 billion in 2019. In 2019 Russia was the origin of ca. 40% of EU imports of gas and 27% of EU imports of oil. Due to the large value these imports, EU’s trade deficit with Russia (€ 57 billion in 2019) is only second to EU’s trade deficit with China.

The issue here, of course, is the fact that this trade is represented for a whole Europe, 4 of the major nations of her, constitute a bulk of G-7. By far the most important dynamics here is this: 

EU-Russia bilateral trade in goods peaked in 2012, dropping by 43% between 2012 and 2016 from two-way €322 billion in 2012 to €183 billion in 2016. Since 2016, bilateral trade has partially recovered. However, Overall EU exports to Russia were in 2019 25% lower than in 2012, agri-food exports were 38% lower.

These are the effects of a non-stop trade war (sanctions) on Russia supported by all those Europeans and, quoting, Karen Shakhnazarov, "sanctions are good for Russia", because sanctions allow increasing decoupling from EU, including by means of import substitution, and the only way Europe can still retain interest for Russians is EU being a market, which will increasingly, due to a sheer stupidity of EU bureaucracy, will be destabilized due to confluence of macroeconomic and cultural factors. Russia is just fine dealing with Europeans on a bilateral level. But here is another dynamics to consider:

Look at this dynamics, which brought Russia-Chinese trade to $107 billion in 2019 and continues to grow, eventually projected to hit volume of $200 billion by 2024. Comparable to the volume of trade of Russia with Europe, which hates Russian guts and will behave as the US lap dog in the future. So, Russia's choice is quite obvious here. Especially when one considers a puny trade relations between the US and Russia and Russia having a full grasp of US enmity towards herself. Aw, just look at these numbers:

Russia ranked No. 28 in total trade value through March with a total of $6.61 billion. Exports totaled $1.18 billion and Imports totaled $5.43 billion, a deficit of $4.25 billion.

Pretty much sums it up, doesn't it? So, Trump wants to exclude China from "international community" by holding this gathering which decides nothing and is worthless in terms of any practical solutions to an unfolding catastrophe which is global economic crisis. So, anyone can explain what Russia is to gain, other than some photo-ops for Trump, from this meeting? Why should Vladimir Putin even be there? Moscow and New Delhi have a direct line and can solve their issues by talking directly, Europe, frankly, is economically suicidal, Australia is a non-entity for Russia, so why? I don't know, but Trump, evidently thinks that this is a good idea. I think it is a waste of time, because the settling of global issues must happen first between G-3: China, US and Russia. Until something is decided within this triangle no other meetings will produce any sensible world order which will reasonably satisfy everyone. The United States is not ready to deal with this issue yet, but US has only two options here: war and getting back to the reality. What will be this choice we don't know yet, hopefully the latter one.