Over the past 6 months, there's a total of 3 validators have been replaced in the top 10 validators list. Out of the 3 validators, all of them were replaced in the month of Dec'2021:

• Mosaic replaced by Staked in 1st Dec,
• Luna maximalist replaced by NOD Games in 7th Dec,
• mainnet-validator replaced by DSRC-CHAIS in 10th Dec.

I was only able to identify 3/6 validators above to look into reasons that could explain the reason behind their increase:

Mosaic (Mosaic Investments Korea) : http://www.mosaic.kr/en/ NOD Games (Blockchain Gaming) : https://www.nodgames.com/ Staked (Staking & Lending) : https://staked.us

It is likely that NOD Games' increase in voting power is related to the recent craze in P2E/Gaming/Metaverse. Perhaps this maybe a sign for something upcoming in Terra related to P2E?

In addition, the increase in popularity of blockchain and L1 altcoins such as FTM/AVAX/LUNA has also led to more companies starting to help retail investors(or even institutions) gain access to DeFi staking/lending such as Staked.

For the top 10 validators, the total amount of Luna delegated has been on the decline by 12%, from 140M on 13th Oct 2021 to 123M on 11th Dec 2021. However, if we were to look at the total Luna delegated by the top 10 validators as a percentage of the total Luna delegated, it is shown that the total percentage has been on the increase from 42.1% to 46.3%.

This suggests that there's a decrease in decentralization of voting power on the terra blockchain towards the top 10 validators. Given that a 12% decrease in total luna delegated corresponded to a 4% increase in percentage delegated by the top 10 validators, it is an effective decrease of 16% of decentralization.

In comparison with other PoS Blockchains:

• Luna: Top 10 validators constitutes 46.3% of total LUNA delegated(~37.1% of Circulating Supply)
• Matic: Top 10 validators constitutes 77.7% of total MATIC delegated(27.46% of Circulating Supply)
• Avalanche: Top 10 validators constitutes 13% of total AVAX delegated(58.21% of Circulating Supply)
• Solana: Top 10 validators constitutes 21.5% of total SOL delegated(75.99% of Circulating Supply)
• Fantom: Top 10 validators constitutes 76.1% of total FTM delegated(63.82% of Circulating Supply)

*data were all retrieved from https://www.stakingrewards.com/

It looks like Luna seems close to the average percentage when compared with other blockchains. Do note that this analysis only takes into account the proportion of delegation by the top 10 validators over the total amount delegated. There could be other factors affecting whether a blockchain is truly "decentralized" such as barrier to entry using expensive hardware, etc.

The top 10 validators have a voting power ranging between 6.5M Luna to 27.2 Luna over the past 2 months. This translates to roughly 2.4% to 9.4% of the total amount of Luna delegated. Among the top 3 validators, Staking Fund and B-Harvest both increased by 0.5M Luna delegated while Orion Money dropped by about 2.2M.

This large drop in Luna delegated to Orion could be attributed to the Orion Airdrop collection going live on 16th of Nov. The sharpest decline occurred between 15th Nov and 21st Nov which was right after the Orion airdrop collection date.